diff --git a/.github/scripts/python.sh b/.github/scripts/python.sh
index c72e9abd6..08b8084a0 100644
--- a/.github/scripts/python.sh
+++ b/.github/scripts/python.sh
@@ -39,8 +39,6 @@ function install_dependencies()
   if [ "${GTSAM_WITH_TBB:-OFF}" == "ON" ]; then
     install_tbb
   fi
-
-  $PYTHON -m pip install -r $GITHUB_WORKSPACE/python/requirements.txt
 }
 
 function build()
diff --git a/.github/workflows/build-python.yml b/.github/workflows/build-python.yml
index 480c791dc..91bc4e80a 100644
--- a/.github/workflows/build-python.yml
+++ b/.github/workflows/build-python.yml
@@ -109,10 +109,13 @@ jobs:
         with:
           swap-size-gb: 6
 
-      - name: Install Dependencies
+      - name: Install System Dependencies
         run: |
           bash .github/scripts/python.sh -d
 
+      - name: Install Python Dependencies
+        run: python$PYTHON_VERSION -m pip install -r python/dev_requirements.txt
+
       - name: Build
         run: |
           bash .github/scripts/python.sh -b
diff --git a/.github/workflows/build-windows.yml b/.github/workflows/build-windows.yml
index a1d232b2a..f0568394f 100644
--- a/.github/workflows/build-windows.yml
+++ b/.github/workflows/build-windows.yml
@@ -150,7 +150,10 @@ jobs:
           # cmake --build build -j4 --config ${{ matrix.build_type }} --target check.dynamics_unstable
           # Compile. Fail with exception
           # cmake --build build -j4 --config ${{ matrix.build_type }} --target check.nonlinear_unstable
-          # Compilation error
+          # Compile. Fail with exception
           # cmake --build build -j4 --config ${{ matrix.build_type }} --target check.slam_unstable
-          # Compilation error
+          # Compile. Fail with exception
           # cmake --build build -j4 --config ${{ matrix.build_type }} --target check.partition
+
+          # Run all tests
+          # cmake --build build -j1 --config ${{ matrix.build_type }} --target check
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 309cc7c4e..63c7f9e54 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,11 +1,5 @@
 cmake_minimum_required(VERSION 3.0)
 
-# new feature to Cmake Version > 2.8.12
-# Mac ONLY. Define Relative Path on Mac OS
-if(NOT DEFINED CMAKE_MACOSX_RPATH)
-  set(CMAKE_MACOSX_RPATH 0)
-endif()
-
 # Set the version number for the library
 set (GTSAM_VERSION_MAJOR 4)
 set (GTSAM_VERSION_MINOR 3)
diff --git a/INSTALL.md b/INSTALL.md
index f148e3718..10bee196c 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -182,7 +182,7 @@ Here are some tips to get the best possible performance out of GTSAM.
     optimization by 30-50%. Please note that this may not be true for very small 
     problems where the overhead of dispatching work to multiple threads outweighs
     the benefit. We recommend that you benchmark your problem with/without TBB.
-3. Add `-march=native` to `GTSAM_CMAKE_CXX_FLAGS`. A performance gain of
+3. Use `GTSAM_BUILD_WITH_MARCH_NATIVE`. A performance gain of
     25-30% can be expected on modern processors. Note that this affects the portability
     of your executable. It may not run when copied to another system with older/different
     processor architecture.
diff --git a/docker/ubuntu-gtsam-python/Dockerfile b/docker/ubuntu-gtsam-python/Dockerfile
index 85eed4d4e..4a7c4b37f 100644
--- a/docker/ubuntu-gtsam-python/Dockerfile
+++ b/docker/ubuntu-gtsam-python/Dockerfile
@@ -6,9 +6,6 @@ FROM borglab/ubuntu-gtsam:bionic
 # Install pip
 RUN apt-get install -y python3-pip python3-dev
 
-# Install python wrapper requirements
-RUN python3 -m pip install -U -r /usr/src/gtsam/python/requirements.txt
-
 # Run cmake again, now with python toolbox on
 WORKDIR /usr/src/gtsam/build
 RUN cmake \
diff --git a/gtsam/base/serialization.h b/gtsam/base/serialization.h
index e615afe83..18612bc22 100644
--- a/gtsam/base/serialization.h
+++ b/gtsam/base/serialization.h
@@ -17,6 +17,7 @@
  * @date Feb 7, 2012
  */
 
+#ifdef GTSAM_ENABLE_BOOST_SERIALIZATION
 #pragma once
 
 #include <Eigen/Core>
@@ -270,3 +271,4 @@ void deserializeBinary(const std::string& serialized, T& output,
 ///@}
 
 }  // namespace gtsam
+#endif
diff --git a/gtsam/discrete/AlgebraicDecisionTree.h b/gtsam/discrete/AlgebraicDecisionTree.h
index 20ab4bd68..9f55f3b63 100644
--- a/gtsam/discrete/AlgebraicDecisionTree.h
+++ b/gtsam/discrete/AlgebraicDecisionTree.h
@@ -36,7 +36,7 @@ namespace gtsam {
    * @ingroup discrete
    */
   template <typename L>
-  class GTSAM_EXPORT AlgebraicDecisionTree : public DecisionTree<L, double> {
+  class AlgebraicDecisionTree : public DecisionTree<L, double> {
     /**
      * @brief Default method used by `labelFormatter` or `valueFormatter` when
      * printing.
diff --git a/gtsam/linear/SubgraphBuilder.h b/gtsam/linear/SubgraphBuilder.h
index aafba9306..f9ddd4c9a 100644
--- a/gtsam/linear/SubgraphBuilder.h
+++ b/gtsam/linear/SubgraphBuilder.h
@@ -182,7 +182,7 @@ GaussianFactorGraph buildFactorSubgraph(const GaussianFactorGraph &gfg,
 
 /** Split the graph into a subgraph and the remaining edges. 
  * Note that the remaining factorgraph has null factors. */
-std::pair<GaussianFactorGraph, GaussianFactorGraph> splitFactorGraph(
+std::pair<GaussianFactorGraph, GaussianFactorGraph> GTSAM_EXPORT splitFactorGraph(
     const GaussianFactorGraph &factorGraph, const Subgraph &subgraph);
 
 }  // namespace gtsam
diff --git a/gtsam/nonlinear/NonlinearFactor.h b/gtsam/nonlinear/NonlinearFactor.h
index 57c4a00eb..725117748 100644
--- a/gtsam/nonlinear/NonlinearFactor.h
+++ b/gtsam/nonlinear/NonlinearFactor.h
@@ -46,7 +46,7 @@ namespace gtsam {
  * Had to use the static_cast of a nullptr, because the compiler is not able to
  * deduce the type of the nullptr when expanding the evaluateError templates.
  */
-#define OptionalNone static_cast<Matrix*>(nullptr)
+#define OptionalNone static_cast<gtsam::Matrix*>(nullptr)
 
 /** This typedef will be used everywhere boost::optional<Matrix&> reference was used
  * previously. This is used to indicate that the Jacobian is optional. In the future
diff --git a/gtsam/sfm/TranslationRecovery.h b/gtsam/sfm/TranslationRecovery.h
index 44a5ef43e..4848d7cfa 100644
--- a/gtsam/sfm/TranslationRecovery.h
+++ b/gtsam/sfm/TranslationRecovery.h
@@ -48,7 +48,7 @@ namespace gtsam {
 // where s is an arbitrary scale that can be supplied, default 1.0. Hence, two
 // versions are supplied below corresponding to whether we have initial values
 // or not.
-class TranslationRecovery {
+class GTSAM_EXPORT TranslationRecovery {
  public:
   using KeyPair = std::pair<Key, Key>;
   using TranslationEdges = std::vector<BinaryMeasurement<Unit3>>;
diff --git a/gtsam_unstable/geometry/Event.h b/gtsam_unstable/geometry/Event.h
index a4055d038..a3c907646 100644
--- a/gtsam_unstable/geometry/Event.h
+++ b/gtsam_unstable/geometry/Event.h
@@ -34,7 +34,7 @@ namespace gtsam {
  * SLAM, where we have "time of arrival" measurements at a set of sensors. The
  * TOA functor below provides a measurement function for those applications.
  */
-class Event {
+class GTSAM_UNSTABLE_EXPORT Event {
   double time_;      ///< Time event was generated
   Point3 location_;  ///< Location at time event was generated
 
@@ -62,10 +62,10 @@ class Event {
   }
 
   /** print with optional string */
-  GTSAM_UNSTABLE_EXPORT void print(const std::string& s = "") const;
+  void print(const std::string& s = "") const;
 
   /** equals with an tolerance */
-  GTSAM_UNSTABLE_EXPORT bool equals(const Event& other,
+  bool equals(const Event& other,
                                     double tol = 1e-9) const;
 
   /// Updates a with tangent space delta
diff --git a/gtsam_unstable/partition/GenericGraph.h b/gtsam_unstable/partition/GenericGraph.h
index bcfd77336..a7f2c1ea3 100644
--- a/gtsam_unstable/partition/GenericGraph.h
+++ b/gtsam_unstable/partition/GenericGraph.h
@@ -14,6 +14,7 @@
 #include <stdexcept>
 #include <string>
 #include <memory>
+#include <gtsam_unstable/dllexport.h>
 
 #include "PartitionWorkSpace.h"
 
@@ -49,7 +50,7 @@ namespace gtsam { namespace partition {
   typedef std::vector<sharedGenericFactor2D> GenericGraph2D;
 
   /** merge nodes in DSF using constraints captured by the given graph */
-  std::list<std::vector<size_t> > findIslands(const GenericGraph2D& graph, const std::vector<size_t>& keys, WorkSpace& workspace,
+  std::list<std::vector<size_t> > GTSAM_UNSTABLE_EXPORT findIslands(const GenericGraph2D& graph, const std::vector<size_t>& keys, WorkSpace& workspace,
       const int minNrConstraintsPerCamera, const int minNrConstraintsPerLandmark);
 
   /** eliminate the sensors from generic graph */
@@ -97,11 +98,11 @@ namespace gtsam { namespace partition {
   typedef std::vector<sharedGenericFactor3D> GenericGraph3D;
 
   /** merge nodes in DSF using constraints captured by the given graph */
-  std::list<std::vector<size_t> > findIslands(const GenericGraph3D& graph, const std::vector<size_t>& keys, WorkSpace& workspace,
+  std::list<std::vector<size_t> > GTSAM_UNSTABLE_EXPORT findIslands(const GenericGraph3D& graph, const std::vector<size_t>& keys, WorkSpace& workspace,
       const size_t minNrConstraintsPerCamera, const size_t minNrConstraintsPerLandmark);
 
   /** eliminate the sensors from generic graph */
-  void reduceGenericGraph(const GenericGraph3D& graph, const std::vector<size_t>& cameraKeys,  const std::vector<size_t>& landmarkKeys,
+  void GTSAM_UNSTABLE_EXPORT reduceGenericGraph(const GenericGraph3D& graph, const std::vector<size_t>& cameraKeys,  const std::vector<size_t>& landmarkKeys,
       const std::vector<int>& dictionary,  GenericGraph3D& reducedGraph);
 
   /** check whether the 3D graph is singular (under constrained) */
diff --git a/gtsam_unstable/partition/tests/CMakeLists.txt b/gtsam_unstable/partition/tests/CMakeLists.txt
index 0b918e497..4ca6b9186 100644
--- a/gtsam_unstable/partition/tests/CMakeLists.txt
+++ b/gtsam_unstable/partition/tests/CMakeLists.txt
@@ -1,6 +1,6 @@
 set(ignore_test "testNestedDissection.cpp")
 
-if (NOT GTSAM_USE_BOOST_FEATURES)
+if (NOT GTSAM_USE_BOOST_FEATURES OR MSVC)
 	list(APPEND ignore_test "testFindSeparator.cpp")
 endif()
 
diff --git a/gtsam_unstable/slam/ProjectionFactorPPPC.h b/gtsam_unstable/slam/ProjectionFactorPPPC.h
index 5b6a83a33..df63330df 100644
--- a/gtsam_unstable/slam/ProjectionFactorPPPC.h
+++ b/gtsam_unstable/slam/ProjectionFactorPPPC.h
@@ -32,7 +32,7 @@ namespace gtsam {
    * @ingroup slam
    */
 template <class POSE, class LANDMARK, class CALIBRATION = Cal3_S2>
-class GTSAM_UNSTABLE_EXPORT ProjectionFactorPPPC
+class ProjectionFactorPPPC
     : public NoiseModelFactorN<POSE, POSE, LANDMARK, CALIBRATION> {
  protected:
   Point2 measured_;  ///< 2D measurement
diff --git a/gtsam_unstable/slam/SmartProjectionPoseFactorRollingShutter.h b/gtsam_unstable/slam/SmartProjectionPoseFactorRollingShutter.h
index 4af0be751..4a2047ee1 100644
--- a/gtsam_unstable/slam/SmartProjectionPoseFactorRollingShutter.h
+++ b/gtsam_unstable/slam/SmartProjectionPoseFactorRollingShutter.h
@@ -42,7 +42,7 @@ namespace gtsam {
  * @ingroup slam
  */
 template <class CAMERA>
-class GTSAM_UNSTABLE_EXPORT SmartProjectionPoseFactorRollingShutter
+class SmartProjectionPoseFactorRollingShutter
     : public SmartProjectionFactor<CAMERA> {
  private:
   typedef SmartProjectionFactor<CAMERA> Base;
diff --git a/gtsam_unstable/slam/tests/testSmartStereoProjectionPoseFactor.cpp b/gtsam_unstable/slam/tests/testSmartStereoProjectionPoseFactor.cpp
index 1eceb8061..872cd2dea 100644
--- a/gtsam_unstable/slam/tests/testSmartStereoProjectionPoseFactor.cpp
+++ b/gtsam_unstable/slam/tests/testSmartStereoProjectionPoseFactor.cpp
@@ -1441,14 +1441,14 @@ TEST( SmartStereoProjectionPoseFactor, HessianWithRotationNonDegenerate ) {
   std::shared_ptr<GaussianFactor> hessianFactorRotTran =
       smartFactor->linearize(tranValues);
 
-  // Hessian is invariant to rotations and translations in the degenerate case
-  EXPECT(
-      assert_equal(hessianFactor->information(),
+  double error;
 #ifdef GTSAM_USE_EIGEN_MKL
-          hessianFactorRotTran->information(), 1e-5));
+  error = 1e-5;
 #else
-          hessianFactorRotTran->information(), 1e-6));
+  error = 1e-6;
 #endif
+  // Hessian is invariant to rotations and translations in the degenerate case
+  EXPECT(assert_equal(hessianFactor->information(), hessianFactorRotTran->information(), error));
 }
 
 /* ************************************************************************* */
diff --git a/python/CMakeLists.txt b/python/CMakeLists.txt
index 2b2abf507..f874c2f21 100644
--- a/python/CMakeLists.txt
+++ b/python/CMakeLists.txt
@@ -1,3 +1,4 @@
+set(PROJECT_PYTHON_SOURCE_DIR ${PROJECT_SOURCE_DIR}/python)
 set(GTSAM_PYTHON_BUILD_DIRECTORY ${PROJECT_BINARY_DIR}/python)
 
 if (NOT GTSAM_BUILD_PYTHON)
@@ -6,11 +7,11 @@ endif()
 
 # Generate setup.py.
 file(READ "${PROJECT_SOURCE_DIR}/README.md" README_CONTENTS)
-configure_file(${PROJECT_SOURCE_DIR}/python/setup.py.in
+configure_file(${PROJECT_PYTHON_SOURCE_DIR}/setup.py.in
                 ${GTSAM_PYTHON_BUILD_DIRECTORY}/setup.py)
 
 # Supply MANIFEST.in for older versions of Python
-file(COPY ${PROJECT_SOURCE_DIR}/python/MANIFEST.in
+file(COPY ${PROJECT_PYTHON_SOURCE_DIR}/MANIFEST.in
      DESTINATION ${GTSAM_PYTHON_BUILD_DIRECTORY})
 
 set(WRAP_BUILD_TYPE_POSTFIXES ${GTSAM_BUILD_TYPE_POSTFIXES})
@@ -99,7 +100,7 @@ pybind_wrap(${GTSAM_PYTHON_TARGET} # target
             "gtsam" # module_name
             "gtsam" # top_namespace
             "${ignore}" # ignore_classes
-            ${PROJECT_SOURCE_DIR}/python/gtsam/gtsam.tpl
+            ${PROJECT_PYTHON_SOURCE_DIR}/gtsam/gtsam.tpl
             gtsam # libs
             "gtsam;gtsam_header" # dependencies
             ${GTSAM_ENABLE_BOOST_SERIALIZATION} # use_boost_serialization
@@ -178,7 +179,7 @@ if(GTSAM_UNSTABLE_BUILD_PYTHON)
             "gtsam_unstable" # module_name
             "gtsam" # top_namespace
             "${ignore}" # ignore_classes
-            ${PROJECT_SOURCE_DIR}/python/gtsam_unstable/gtsam_unstable.tpl
+            ${PROJECT_PYTHON_SOURCE_DIR}/gtsam_unstable/gtsam_unstable.tpl
             gtsam_unstable # libs
             "gtsam_unstable;gtsam_unstable_header" # dependencies
             ${GTSAM_ENABLE_BOOST_SERIALIZATION} # use_boost_serialization
diff --git a/python/README.md b/python/README.md
index 278d62094..e81be74fc 100644
--- a/python/README.md
+++ b/python/README.md
@@ -16,7 +16,7 @@ For instructions on updating the version of the [wrap library](https://github.co
 - This wrapper needs `pyparsing(>=2.4.2)`, and `numpy(>=1.11.0)`. These can be installed as follows:
 
   ```bash
-  pip install -r <gtsam_folder>/python/requirements.txt
+  pip install -r <gtsam_folder>/python/dev_requirements.txt
   ```
 
 ## Install
diff --git a/python/dev_requirements.txt b/python/dev_requirements.txt
new file mode 100644
index 000000000..6970ee613
--- /dev/null
+++ b/python/dev_requirements.txt
@@ -0,0 +1,2 @@
+-r requirements.txt
+pyparsing>=2.4.2
\ No newline at end of file
diff --git a/python/requirements.txt b/python/requirements.txt
index 481d27d8e..099cc80d6 100644
--- a/python/requirements.txt
+++ b/python/requirements.txt
@@ -1,2 +1 @@
 numpy>=1.11.0
-pyparsing>=2.4.2
diff --git a/python/setup.py.in b/python/setup.py.in
index 9aa4b71f4..e15e39075 100644
--- a/python/setup.py.in
+++ b/python/setup.py.in
@@ -1,19 +1,17 @@
 """Setup file to install the GTSAM package."""
 
-try:
-    from setuptools import setup, find_packages
-except ImportError:
-    from distutils.core import setup, find_packages
+from setuptools import setup, find_namespace_packages
 
-packages = find_packages(where=".")
+packages = find_namespace_packages(
+    where=".",
+    exclude=('build', 'build.*', 'CMakeFiles', 'CMakeFiles.*',
+             'gtsam.notebooks', '*.preamble', '*.specializations', 'dist'))
 print("PACKAGES: ", packages)
 
 package_data = {
     '': [
         "./*.so",
-        "./*.dll",
-        "Data/*"  # Add the data files to the package
-        "Data/**/*"  # Add the data files in subdirectories
+        "./*.dll"
     ]
 }
 
@@ -41,7 +39,6 @@ setup(
         'Operating System :: Microsoft :: Windows',
         'Operating System :: POSIX',
         'License :: OSI Approved :: BSD License',
-        'Programming Language :: Python :: 2',
         'Programming Language :: Python :: 3',
     ],
     packages=packages,
diff --git a/wrap/.gitignore b/wrap/.gitignore
index 9f79deafa..de16b118d 100644
--- a/wrap/.gitignore
+++ b/wrap/.gitignore
@@ -5,6 +5,8 @@ __pycache__/
 *dist*
 *.egg-info
 
+**/.DS_Store
+
 # Files related to code coverage stats
 **/.coverage
 
diff --git a/wrap/pybind11/.clang-tidy b/wrap/pybind11/.clang-tidy
index d945a4a27..23018386c 100644
--- a/wrap/pybind11/.clang-tidy
+++ b/wrap/pybind11/.clang-tidy
@@ -63,6 +63,8 @@ Checks: |
   -bugprone-unused-raii,
 
 CheckOptions:
+- key:             modernize-use-equals-default.IgnoreMacros
+  value:           false
 - key:             performance-for-range-copy.WarnOnAllAutoCopies
   value:           true
 - key:             performance-inefficient-string-concatenation.StrictMode
diff --git a/wrap/pybind11/.codespell-ignore-lines b/wrap/pybind11/.codespell-ignore-lines
new file mode 100644
index 000000000..2a01d63eb
--- /dev/null
+++ b/wrap/pybind11/.codespell-ignore-lines
@@ -0,0 +1,24 @@
+template <op_id id, op_type ot, typename L = undefined_t, typename R = undefined_t>
+    template <typename ThisT>
+        auto &this_ = static_cast<ThisT &>(*this);
+                if (load_impl<ThisT>(temp, false)) {
+        ssize_t nd = 0;
+        auto trivial = broadcast(buffers, nd, shape);
+        auto ndim = (size_t) nd;
+    int nd;
+    ssize_t ndim() const { return detail::array_proxy(m_ptr)->nd; }
+        using op = op_impl<id, ot, Base, L_type, R_type>;
+template <op_id id, op_type ot, typename L, typename R>
+    template <detail::op_id id, detail::op_type ot, typename L, typename R, typename... Extra>
+    class_ &def(const detail::op_<id, ot, L, R> &op, const Extra &...extra) {
+    class_ &def_cast(const detail::op_<id, ot, L, R> &op, const Extra &...extra) {
+@pytest.mark.parametrize("access", ["ro", "rw", "static_ro", "static_rw"])
+struct IntStruct {
+    explicit IntStruct(int v) : value(v){};
+    ~IntStruct() { value = -value; }
+    IntStruct(const IntStruct &) = default;
+    IntStruct &operator=(const IntStruct &) = default;
+    py::class_<IntStruct>(m, "IntStruct").def(py::init([](const int i) { return IntStruct(i); }));
+    py::implicitly_convertible<int, IntStruct>();
+    m.def("test", [](int expected, const IntStruct &in) {
+        [](int expected, const IntStruct &in) {
diff --git a/wrap/pybind11/.github/CONTRIBUTING.md b/wrap/pybind11/.github/CONTRIBUTING.md
index 00b1fea4c..ad7974395 100644
--- a/wrap/pybind11/.github/CONTRIBUTING.md
+++ b/wrap/pybind11/.github/CONTRIBUTING.md
@@ -235,8 +235,8 @@ directory inside your pybind11 git clone. Files will be modified in place,
 so you can use git to monitor the changes.
 
 ```bash
-docker run --rm -v $PWD:/mounted_pybind11 -it silkeh/clang:13
-apt-get update && apt-get install -y python3-dev python3-pytest
+docker run --rm -v $PWD:/mounted_pybind11 -it silkeh/clang:15-bullseye
+apt-get update && apt-get install -y git python3-dev python3-pytest
 cmake -S /mounted_pybind11/ -B build -DCMAKE_CXX_CLANG_TIDY="$(which clang-tidy);--use-color" -DDOWNLOAD_EIGEN=ON -DDOWNLOAD_CATCH=ON -DCMAKE_CXX_STANDARD=17
 cmake --build build -j 2
 ```
diff --git a/wrap/pybind11/.github/ISSUE_TEMPLATE/bug-report.yml b/wrap/pybind11/.github/ISSUE_TEMPLATE/bug-report.yml
index bd6a9a8e2..4f1e78f33 100644
--- a/wrap/pybind11/.github/ISSUE_TEMPLATE/bug-report.yml
+++ b/wrap/pybind11/.github/ISSUE_TEMPLATE/bug-report.yml
@@ -6,7 +6,8 @@ body:
   - type: markdown
     attributes:
       value: |
-        Maintainers will only make a best effort to triage PRs. Please do your best to make the issue as easy to act on as possible, and only open if clearly a problem with pybind11 (ask first if unsure).
+        Please do your best to make the issue as easy to act on as possible, and only submit here if there is clearly a problem with pybind11 (ask first if unsure). **Note that a reproducer in a PR is much more likely to get immediate attention.**
+
   - type: checkboxes
     id: steps
     attributes:
@@ -20,6 +21,13 @@ body:
         - label: Consider asking first in the [Gitter chat room](https://gitter.im/pybind/Lobby) or in a [Discussion](https:/pybind/pybind11/discussions/new).
           required: false
 
+  - type: input
+    id: version
+    attributes:
+      label: What version (or hash if on master) of pybind11 are you using?
+    validations:
+      required: true
+
   - type: textarea
     id: description
     attributes:
@@ -40,6 +48,14 @@ body:
         The code should be minimal, have no external dependencies, isolate the
         function(s) that cause breakage. Submit matched and complete C++ and
         Python snippets that can be easily compiled and run to diagnose the
-        issue. If possible, make a PR with a new, failing test to give us a
-        starting point to work on!
+        issue. — Note that a reproducer in a PR is much more likely to get
+        immediate attention: failing tests in the pybind11 CI are the best
+        starting point for working out fixes.
       render: text
+
+  - type: input
+    id: regression
+    attributes:
+      label: Is this a regression? Put the last known working version here if it is.
+      description: Put the last known working version here if this is a regression.
+      value: Not a regression
diff --git a/wrap/pybind11/.github/workflows/ci.yml b/wrap/pybind11/.github/workflows/ci.yml
index 412282a4f..48f7c5e93 100644
--- a/wrap/pybind11/.github/workflows/ci.yml
+++ b/wrap/pybind11/.github/workflows/ci.yml
@@ -9,14 +9,19 @@ on:
       - stable
       - v*
 
+permissions: read-all
+
 concurrency:
   group: test-${{ github.ref }}
   cancel-in-progress: true
 
 env:
+  PIP_BREAK_SYSTEM_PACKAGES: 1
   PIP_ONLY_BINARY: numpy
   FORCE_COLOR: 3
   PYTEST_TIMEOUT: 300
+  # For cmake:
+  VERBOSE: 1
 
 jobs:
   # This is the "main" test suite, which tests a large number of different
@@ -25,15 +30,16 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        runs-on: [ubuntu-latest, windows-2022, macos-latest]
+        runs-on: [ubuntu-20.04, windows-2022, macos-latest]
         python:
         - '3.6'
         - '3.9'
         - '3.10'
-        - '3.11-dev'
-        - 'pypy-3.7'
+        - '3.11'
+        - '3.12'
         - 'pypy-3.8'
         - 'pypy-3.9'
+        - 'pypy-3.10'
 
         # Items in here will either be added to the build matrix (if not
         # present), or add new keys to an existing matrix element if all the
@@ -42,12 +48,12 @@ jobs:
         # We support an optional key: args, for cmake args
         include:
           # Just add a key
-          - runs-on: ubuntu-latest
+          - runs-on: ubuntu-20.04
             python: '3.6'
             args: >
               -DPYBIND11_FINDPYTHON=ON
               -DCMAKE_CXX_FLAGS="-D_=1"
-          - runs-on: ubuntu-latest
+          - runs-on: ubuntu-20.04
             python: 'pypy-3.8'
             args: >
               -DPYBIND11_FINDPYTHON=ON
@@ -69,6 +75,7 @@ jobs:
       uses: actions/setup-python@v4
       with:
         python-version: ${{ matrix.python }}
+        allow-prereleases: true
 
     - name: Setup Boost (Linux)
       # Can't use boost + define _
@@ -80,7 +87,7 @@ jobs:
       run: brew install boost
 
     - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.12
+      uses: jwlawson/actions-setup-cmake@v1.14
 
     - name: Cache wheels
       if: runner.os == 'macOS'
@@ -102,10 +109,12 @@ jobs:
       run: python -m pip install pytest-github-actions-annotate-failures
 
     # First build - C++11 mode and inplace
+    # More-or-less randomly adding -DPYBIND11_SIMPLE_GIL_MANAGEMENT=ON here.
     - name: Configure C++11 ${{ matrix.args }}
       run: >
         cmake -S . -B .
         -DPYBIND11_WERROR=ON
+        -DPYBIND11_SIMPLE_GIL_MANAGEMENT=ON
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
         -DCMAKE_CXX_STANDARD=11
@@ -119,7 +128,7 @@ jobs:
 
     - name: C++11 tests
       # TODO: Figure out how to load the DLL on Python 3.8+
-      if: "!(runner.os == 'Windows' && (matrix.python == 3.8 || matrix.python == 3.9 || matrix.python == '3.10' || matrix.python == '3.11-dev' || matrix.python == 'pypy-3.8'))"
+      if: "!(runner.os == 'Windows' && (matrix.python == 3.8 || matrix.python == 3.9 || matrix.python == '3.10' || matrix.python == '3.11' || matrix.python == 'pypy-3.8'))"
       run: cmake --build .  --target cpptest -j 2
 
     - name: Interface test C++11
@@ -129,10 +138,12 @@ jobs:
       run: git clean -fdx
 
     # Second build - C++17 mode and in a build directory
+    # More-or-less randomly adding -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF here.
     - name: Configure C++17
       run: >
         cmake -S . -B build2
         -DPYBIND11_WERROR=ON
+        -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
         -DCMAKE_CXX_STANDARD=17
@@ -146,7 +157,7 @@ jobs:
 
     - name: C++ tests
       # TODO: Figure out how to load the DLL on Python 3.8+
-      if: "!(runner.os == 'Windows' && (matrix.python == 3.8 || matrix.python == 3.9 || matrix.python == '3.10' || matrix.python == '3.11-dev' || matrix.python == 'pypy-3.8'))"
+      if: "!(runner.os == 'Windows' && (matrix.python == 3.8 || matrix.python == 3.9 || matrix.python == '3.10' || matrix.python == '3.11' || matrix.python == 'pypy-3.8'))"
       run: cmake --build build2 --target cpptest
 
     # Third build - C++17 mode with unstable ABI
@@ -158,7 +169,6 @@ jobs:
         -DDOWNLOAD_EIGEN=ON
         -DCMAKE_CXX_STANDARD=17
         -DPYBIND11_INTERNALS_VERSION=10000000
-        "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
         ${{ matrix.args }}
 
     - name: Build (unstable ABI)
@@ -173,7 +183,9 @@ jobs:
     # This makes sure the setup_helpers module can build packages using
     # setuptools
     - name: Setuptools helpers test
-      run: pytest tests/extra_setuptools
+      run: |
+        pip install setuptools
+        pytest tests/extra_setuptools
       if: "!(matrix.runs-on == 'windows-2022')"
 
 
@@ -186,23 +198,23 @@ jobs:
         - python-version: "3.9"
           python-debug: true
           valgrind: true
-        - python-version: "3.11-dev"
+        - python-version: "3.11"
           python-debug: false
 
     name: "🐍 ${{ matrix.python-version }}${{ matrix.python-debug && '-dbg' || '' }} (deadsnakes)${{ matrix.valgrind && ' • Valgrind' || '' }} • x64"
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     steps:
     - uses: actions/checkout@v3
 
     - name: Setup Python ${{ matrix.python-version }} (deadsnakes)
-      uses: deadsnakes/action@v2.1.1
+      uses: deadsnakes/action@v3.0.1
       with:
         python-version: ${{ matrix.python-version }}
         debug: ${{ matrix.python-debug }}
 
     - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.12
+      uses: jwlawson/actions-setup-cmake@v1.14
 
     - name: Valgrind cache
       if: matrix.valgrind
@@ -235,8 +247,6 @@ jobs:
         python -m pip install -r tests/requirements.txt
 
     - name: Configure
-      env:
-        SETUPTOOLS_USE_DISTUTILS: stdlib
       run: >
         cmake -S . -B build
         -DCMAKE_BUILD_TYPE=Debug
@@ -274,18 +284,27 @@ jobs:
           - dev
         std:
           - 11
+        container_suffix:
+          - ""
         include:
           - clang: 5
             std: 14
-          - clang: 10
-            std: 20
           - clang: 10
             std: 17
+          - clang: 11
+            std: 20
+          - clang: 12
+            std: 20
+          - clang: 13
+            std: 20
           - clang: 14
             std: 20
+          - clang: 15
+            std: 20
+            container_suffix: "-bullseye"
 
     name: "🐍 3 • Clang ${{ matrix.clang }} • C++${{ matrix.std }} • x64"
-    container: "silkeh/clang:${{ matrix.clang }}"
+    container: "silkeh/clang:${{ matrix.clang }}${{ matrix.container_suffix }}"
 
     steps:
     - uses: actions/checkout@v3
@@ -318,8 +337,8 @@ jobs:
   # Testing NVCC; forces sources to behave like .cu files
   cuda:
     runs-on: ubuntu-latest
-    name: "🐍 3.8 • CUDA 11.2 • Ubuntu 20.04"
-    container: nvidia/cuda:11.2.2-devel-ubuntu20.04
+    name: "🐍 3.10 • CUDA 12.2 • Ubuntu 22.04"
+    container: nvidia/cuda:12.2.0-devel-ubuntu22.04
 
     steps:
     - uses: actions/checkout@v3
@@ -384,8 +403,9 @@ jobs:
 
   # Testing on CentOS 7 + PGI compilers, which seems to require more workarounds
   centos-nvhpc7:
+    if: ${{ false }}  # JOB DISABLED (NEEDS WORK): https://github.com/pybind/pybind11/issues/4690
     runs-on: ubuntu-latest
-    name: "🐍 3 • CentOS7 / PGI 22.3 • x64"
+    name: "🐍 3 • CentOS7 / PGI 22.9 • x64"
     container: centos:7
 
     steps:
@@ -395,7 +415,7 @@ jobs:
       run: yum update -y && yum install -y epel-release && yum install -y git python3-devel make environment-modules cmake3 yum-utils
 
     - name: Install NVidia HPC SDK
-      run: yum-config-manager --add-repo https://developer.download.nvidia.com/hpc-sdk/rhel/nvhpc.repo && yum -y install nvhpc-22.3
+      run: yum-config-manager --add-repo https://developer.download.nvidia.com/hpc-sdk/rhel/nvhpc.repo && yum -y install nvhpc-22.9
 
     # On CentOS 7, we have to filter a few tests (compiler internal error)
     # and allow deeper template recursion (not needed on CentOS 8 with a newer
@@ -405,12 +425,12 @@ jobs:
       shell: bash
       run: |
         source /etc/profile.d/modules.sh
-        module load /opt/nvidia/hpc_sdk/modulefiles/nvhpc/22.3
+        module load /opt/nvidia/hpc_sdk/modulefiles/nvhpc/22.9
         cmake3 -S . -B build -DDOWNLOAD_CATCH=ON \
                             -DCMAKE_CXX_STANDARD=11 \
                             -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)") \
                             -DCMAKE_CXX_FLAGS="-Wc,--pending_instantiations=0" \
-                            -DPYBIND11_TEST_FILTER="test_smart_ptr.cpp;test_virtual_functions.cpp"
+                            -DPYBIND11_TEST_FILTER="test_smart_ptr.cpp"
 
     # Building before installing Pip should produce a warning but not an error
     - name: Build
@@ -437,14 +457,14 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        gcc:
-          - 7
-          - latest
-        std:
-          - 11
         include:
-          - gcc: 10
-            std: 20
+          - { gcc: 7, std: 11 }
+          - { gcc: 7, std: 17 }
+          - { gcc: 8, std: 14 }
+          - { gcc: 8, std: 17 }
+          - { gcc: 10, std: 17 }
+          - { gcc: 11, std: 20 }
+          - { gcc: 12, std: 20 }
 
     name: "🐍 3 • GCC ${{ matrix.gcc }} • C++${{ matrix.std }}• x64"
     container: "gcc:${{ matrix.gcc }}"
@@ -459,7 +479,7 @@ jobs:
       run: python3 -m pip install --upgrade pip
 
     - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.12
+      uses: jwlawson/actions-setup-cmake@v1.14
 
     - name: Configure
       shell: bash
@@ -482,6 +502,24 @@ jobs:
     - name: Interface test
       run: cmake --build build --target test_cmake_build
 
+    - name: Configure - Exercise cmake -DPYBIND11_TEST_OVERRIDE
+      if: matrix.gcc == '12'
+      shell: bash
+      run: >
+        cmake -S . -B build_partial
+        -DPYBIND11_WERROR=ON
+        -DDOWNLOAD_CATCH=ON
+        -DCMAKE_CXX_STANDARD=${{ matrix.std }}
+        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
+        "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
+
+    - name: Build - Exercise cmake -DPYBIND11_TEST_OVERRIDE
+      if: matrix.gcc == '12'
+      run: cmake --build build_partial -j 2
+
+    - name: Python tests - Exercise cmake -DPYBIND11_TEST_OVERRIDE
+      if: matrix.gcc == '12'
+      run: cmake --build build_partial --target pytest
 
   # Testing on ICC using the oneAPI apt repo
   icc:
@@ -731,6 +769,9 @@ jobs:
             args: -DCMAKE_CXX_STANDARD=20
           - python: 3.8
             args: -DCMAKE_CXX_STANDARD=17
+          - python: 3.7
+            args: -DCMAKE_CXX_STANDARD=14
+
 
     name: "🐍 ${{ matrix.python }} • MSVC 2019 • x86 ${{ matrix.args }}"
     runs-on: windows-2019
@@ -745,10 +786,10 @@ jobs:
         architecture: x86
 
     - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.12
+      uses: jwlawson/actions-setup-cmake@v1.14
 
     - name: Prepare MSVC
-      uses: ilammy/msvc-dev-cmd@v1.10.0
+      uses: ilammy/msvc-dev-cmd@v1.12.1
       with:
         arch: x86
 
@@ -798,10 +839,10 @@ jobs:
         architecture: x86
 
     - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.12
+      uses: jwlawson/actions-setup-cmake@v1.14
 
     - name: Prepare MSVC
-      uses: ilammy/msvc-dev-cmd@v1.10.0
+      uses: ilammy/msvc-dev-cmd@v1.12.1
       with:
         arch: x86
 
@@ -849,7 +890,7 @@ jobs:
         python3 -m pip install -r tests/requirements.txt
 
     - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.12
+      uses: jwlawson/actions-setup-cmake@v1.14
 
     - name: Configure C++20
       run: >
@@ -871,6 +912,21 @@ jobs:
     - name: Interface test C++20
       run: cmake --build build --target test_cmake_build
 
+    - name: Configure C++20 - Exercise cmake -DPYBIND11_TEST_OVERRIDE
+      run: >
+        cmake -S . -B build_partial
+        -DPYBIND11_WERROR=ON
+        -DDOWNLOAD_CATCH=ON
+        -DDOWNLOAD_EIGEN=ON
+        -DCMAKE_CXX_STANDARD=20
+        "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
+
+    - name: Build C++20 - Exercise cmake -DPYBIND11_TEST_OVERRIDE
+      run: cmake --build build_partial -j 2
+
+    - name: Python tests - Exercise cmake -DPYBIND11_TEST_OVERRIDE
+      run: cmake --build build_partial --target pytest
+
   mingw:
     name: "🐍 3 • windows-latest • ${{ matrix.sys }}"
     runs-on: windows-latest
@@ -905,7 +961,7 @@ jobs:
     - name: Configure C++11
       # LTO leads to many undefined reference like
       # `pybind11::detail::function_call::function_call(pybind11::detail::function_call&&)
-      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=11 -DDOWNLOAD_CATCH=ON -S . -B build
+      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=11 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON -S . -B build
 
     - name: Build C++11
       run: cmake --build build -j 2
@@ -923,7 +979,7 @@ jobs:
       run: git clean -fdx
 
     - name: Configure C++14
-      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=14 -DDOWNLOAD_CATCH=ON -S . -B build2
+      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=14 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON -S . -B build2
 
     - name: Build C++14
       run: cmake --build build2 -j 2
@@ -941,7 +997,7 @@ jobs:
       run: git clean -fdx
 
     - name: Configure C++17
-      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=17 -DDOWNLOAD_CATCH=ON -S . -B build3
+      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=17 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON -S . -B build3
 
     - name: Build C++17
       run: cmake --build build3 -j 2
@@ -954,3 +1010,156 @@ jobs:
 
     - name: Interface test C++17
       run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build3 --target test_cmake_build
+
+  windows_clang:
+
+    strategy:
+      matrix:
+        os: [windows-latest]
+        python: ['3.10']
+
+    runs-on: "${{ matrix.os }}"
+
+    name: "🐍 ${{ matrix.python }} • ${{ matrix.os }} • clang-latest"
+
+    steps:
+      - name: Show env
+        run: env
+
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Set up Clang
+        uses: egor-tensin/setup-clang@v1
+
+      - name: Setup Python ${{ matrix.python }}
+        uses: actions/setup-python@v4
+        with:
+          python-version: ${{ matrix.python }}
+
+      - name: Update CMake
+        uses: jwlawson/actions-setup-cmake@v1.14
+
+      - name: Install ninja-build tool
+        uses: seanmiddleditch/gha-setup-ninja@v3
+
+      - name: Run pip installs
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install -r tests/requirements.txt
+
+      - name: Show Clang++ version
+        run: clang++ --version
+
+      - name: Show CMake version
+        run: cmake --version
+
+      # TODO: WERROR=ON
+      - name: Configure Clang
+        run: >
+          cmake -G Ninja -S . -B .
+          -DPYBIND11_WERROR=OFF
+          -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF
+          -DDOWNLOAD_CATCH=ON
+          -DDOWNLOAD_EIGEN=ON
+          -DCMAKE_CXX_COMPILER=clang++
+          -DCMAKE_CXX_STANDARD=17
+
+      - name: Build
+        run: cmake --build . -j 2
+
+      - name: Python tests
+        run: cmake --build . --target pytest -j 2
+
+      - name: C++ tests
+        run: cmake --build . --target cpptest -j 2
+
+      - name: Interface test
+        run: cmake --build . --target test_cmake_build -j 2
+
+      - name: Clean directory
+        run: git clean -fdx
+
+  macos_brew_install_llvm:
+    name: "macos-latest • brew install llvm"
+    runs-on: macos-latest
+
+    env:
+      # https://apple.stackexchange.com/questions/227026/how-to-install-recent-clang-with-homebrew
+      LDFLAGS: '-L/usr/local/opt/llvm/lib -Wl,-rpath,/usr/local/opt/llvm/lib'
+
+    steps:
+      - name: Update PATH
+        run: echo "/usr/local/opt/llvm/bin" >> $GITHUB_PATH
+
+      - name: Show env
+        run: env
+
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Show Clang++ version before brew install llvm
+        run: clang++ --version
+
+      - name: brew install llvm
+        run: brew install llvm
+
+      - name: Show Clang++ version after brew install llvm
+        run: clang++ --version
+
+      - name: Update CMake
+        uses: jwlawson/actions-setup-cmake@v1.14
+
+      - name: Run pip installs
+        run: |
+          python3 -m pip install --upgrade pip
+          python3 -m pip install -r tests/requirements.txt
+          python3 -m pip install numpy
+          python3 -m pip install scipy
+
+      - name: Show CMake version
+        run: cmake --version
+
+      - name: CMake Configure
+        run: >
+          cmake -S . -B .
+          -DPYBIND11_WERROR=ON
+          -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF
+          -DDOWNLOAD_CATCH=ON
+          -DDOWNLOAD_EIGEN=ON
+          -DCMAKE_CXX_COMPILER=clang++
+          -DCMAKE_CXX_STANDARD=17
+          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
+
+      - name: Build
+        run: cmake --build . -j 2
+
+      - name: Python tests
+        run: cmake --build . --target pytest -j 2
+
+      - name: C++ tests
+        run: cmake --build . --target cpptest -j 2
+
+      - name: Interface test
+        run: cmake --build . --target test_cmake_build -j 2
+
+      - name: CMake Configure - Exercise cmake -DPYBIND11_TEST_OVERRIDE
+        run: >
+          cmake -S . -B build_partial
+          -DPYBIND11_WERROR=ON
+          -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF
+          -DDOWNLOAD_CATCH=ON
+          -DDOWNLOAD_EIGEN=ON
+          -DCMAKE_CXX_COMPILER=clang++
+          -DCMAKE_CXX_STANDARD=17
+          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
+          "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
+
+      - name: Build - Exercise cmake -DPYBIND11_TEST_OVERRIDE
+        run: cmake --build build_partial -j 2
+
+      - name: Python tests - Exercise cmake -DPYBIND11_TEST_OVERRIDE
+        run: cmake --build build_partial --target pytest -j 2
+
+      - name: Clean directory
+        run: git clean -fdx
diff --git a/wrap/pybind11/.github/workflows/configure.yml b/wrap/pybind11/.github/workflows/configure.yml
index edcad4198..ec7cd612d 100644
--- a/wrap/pybind11/.github/workflows/configure.yml
+++ b/wrap/pybind11/.github/workflows/configure.yml
@@ -9,6 +9,14 @@ on:
       - stable
       - v*
 
+permissions:
+  contents: read
+
+env:
+  PIP_BREAK_SYSTEM_PACKAGES: 1
+  # For cmake:
+  VERBOSE: 1
+
 jobs:
   # This tests various versions of CMake in various combinations, to make sure
   # the configure step passes.
@@ -16,22 +24,26 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        runs-on: [ubuntu-latest, macos-latest, windows-latest]
+        runs-on: [ubuntu-20.04, macos-latest, windows-latest]
         arch: [x64]
-        cmake: ["3.23"]
+        cmake: ["3.26"]
 
         include:
-        - runs-on: ubuntu-latest
+        - runs-on: ubuntu-20.04
           arch: x64
-          cmake: 3.4
+          cmake: "3.5"
+
+        - runs-on: ubuntu-20.04
+          arch: x64
+          cmake: "3.27"
 
         - runs-on: macos-latest
           arch: x64
-          cmake: 3.7
+          cmake: "3.7"
 
         - runs-on: windows-2019
           arch: x64 # x86 compilers seem to be missing on 2019 image
-          cmake: 3.18
+          cmake: "3.18"
 
     name: 🐍 3.7 • CMake ${{ matrix.cmake }} • ${{ matrix.runs-on }}
     runs-on: ${{ matrix.runs-on }}
@@ -51,7 +63,7 @@ jobs:
     # An action for adding a specific version of CMake:
     #   https://github.com/jwlawson/actions-setup-cmake
     - name: Setup CMake ${{ matrix.cmake }}
-      uses: jwlawson/actions-setup-cmake@v1.12
+      uses: jwlawson/actions-setup-cmake@v1.14
       with:
         cmake-version: ${{ matrix.cmake }}
 
diff --git a/wrap/pybind11/.github/workflows/format.yml b/wrap/pybind11/.github/workflows/format.yml
index 31d893c47..b8242ee52 100644
--- a/wrap/pybind11/.github/workflows/format.yml
+++ b/wrap/pybind11/.github/workflows/format.yml
@@ -12,8 +12,13 @@ on:
     - stable
     - "v*"
 
+permissions:
+  contents: read
+
 env:
   FORCE_COLOR: 3
+  # For cmake:
+  VERBOSE: 1
 
 jobs:
   pre-commit:
@@ -36,12 +41,12 @@ jobs:
     # in .github/CONTRIBUTING.md and update as needed.
     name: Clang-Tidy
     runs-on: ubuntu-latest
-    container: silkeh/clang:13
+    container: silkeh/clang:15-bullseye
     steps:
     - uses: actions/checkout@v3
 
     - name: Install requirements
-      run: apt-get update && apt-get install -y python3-dev python3-pytest
+      run: apt-get update && apt-get install -y git python3-dev python3-pytest
 
     - name: Configure
       run: >
diff --git a/wrap/pybind11/.github/workflows/labeler.yml b/wrap/pybind11/.github/workflows/labeler.yml
index d2b597968..858a4a0e2 100644
--- a/wrap/pybind11/.github/workflows/labeler.yml
+++ b/wrap/pybind11/.github/workflows/labeler.yml
@@ -3,14 +3,23 @@ on:
   pull_request_target:
     types: [closed]
 
+permissions: {}
+
 jobs:
   label:
     name: Labeler
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pull-requests: write
     steps:
 
     - uses: actions/labeler@main
-      if: github.event.pull_request.merged == true
+      if: >
+        github.event.pull_request.merged == true &&
+        !startsWith(github.event.pull_request.title, 'chore(deps):') &&
+        !startsWith(github.event.pull_request.title, 'ci(fix):') &&
+        !startsWith(github.event.pull_request.title, 'docs(changelog):')
       with:
         repo-token: ${{ secrets.GITHUB_TOKEN }}
         configuration-path: .github/labeler_merged.yml
diff --git a/wrap/pybind11/.github/workflows/pip.yml b/wrap/pybind11/.github/workflows/pip.yml
index 2c16735e1..d6687b441 100644
--- a/wrap/pybind11/.github/workflows/pip.yml
+++ b/wrap/pybind11/.github/workflows/pip.yml
@@ -12,7 +12,11 @@ on:
     types:
     - published
 
+permissions:
+  contents: read
+
 env:
+  PIP_BREAK_SYSTEM_PACKAGES: 1
   PIP_ONLY_BINARY: numpy
 
 jobs:
@@ -98,13 +102,13 @@ jobs:
     - uses: actions/download-artifact@v3
 
     - name: Publish standard package
-      uses: pypa/gh-action-pypi-publish@v1.5.0
+      uses: pypa/gh-action-pypi-publish@release/v1
       with:
         password: ${{ secrets.pypi_password }}
-        packages_dir: standard/
+        packages-dir: standard/
 
     - name: Publish global package
-      uses: pypa/gh-action-pypi-publish@v1.5.0
+      uses: pypa/gh-action-pypi-publish@release/v1
       with:
         password: ${{ secrets.pypi_password_global }}
-        packages_dir: global/
+        packages-dir: global/
diff --git a/wrap/pybind11/.github/workflows/upstream.yml b/wrap/pybind11/.github/workflows/upstream.yml
index a40a6c7d7..dd8a1c960 100644
--- a/wrap/pybind11/.github/workflows/upstream.yml
+++ b/wrap/pybind11/.github/workflows/upstream.yml
@@ -1,112 +1,116 @@
-
 name: Upstream
 
 on:
   workflow_dispatch:
   pull_request:
 
+permissions:
+  contents: read
+
 concurrency:
   group: upstream-${{ github.ref }}
   cancel-in-progress: true
 
 env:
-  PIP_ONLY_BINARY: numpy
+  PIP_BREAK_SYSTEM_PACKAGES: 1
+  PIP_ONLY_BINARY: ":all:"
+  # For cmake:
+  VERBOSE: 1
 
 jobs:
   standard:
-    name: "🐍 3.11 latest internals • ubuntu-latest • x64"
+    name: "🐍 3.12 latest • ubuntu-latest • x64"
     runs-on: ubuntu-latest
+    # Only runs when the  'python dev' label is selected
     if: "contains(github.event.pull_request.labels.*.name, 'python dev')"
 
     steps:
     - uses: actions/checkout@v3
 
-    - name: Setup Python 3.11
+    - name: Setup Python 3.12
       uses: actions/setup-python@v4
       with:
-        python-version: "3.11-dev"
+        python-version: "3.12-dev"
 
-    - name: Setup Boost (Linux)
-      if: runner.os == 'Linux'
+    - name: Setup Boost
       run: sudo apt-get install libboost-dev
 
     - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.12
+      uses: jwlawson/actions-setup-cmake@v1.14
 
-    - name: Prepare env
+    - name: Run pip installs
       run: |
+        python -m pip install --upgrade pip
         python -m pip install -r tests/requirements.txt
 
-    - name: Setup annotations on Linux
-      if: runner.os == 'Linux'
-      run: python -m pip install pytest-github-actions-annotate-failures
+    - name: Show platform info
+      run: |
+        python -m platform
+        cmake --version
+        pip list
 
     # First build - C++11 mode and inplace
     - name: Configure C++11
       run: >
-        cmake -S . -B .
+        cmake -S . -B build11
         -DPYBIND11_WERROR=ON
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
         -DCMAKE_CXX_STANDARD=11
+        -DCMAKE_BUILD_TYPE=Debug
 
     - name: Build C++11
-      run: cmake --build . -j 2
+      run: cmake --build build11 -j 2
 
     - name: Python tests C++11
-      run: cmake --build . --target pytest -j 2
+      run: cmake --build build11 --target pytest -j 2
 
     - name: C++11 tests
-      run: cmake --build .  --target cpptest -j 2
+      run: cmake --build build11  --target cpptest -j 2
 
     - name: Interface test C++11
-      run: cmake --build . --target test_cmake_build
-
-    - name: Clean directory
-      run: git clean -fdx
+      run: cmake --build build11 --target test_cmake_build
 
     # Second build - C++17 mode and in a build directory
     - name: Configure C++17
       run: >
-        cmake -S . -B build2
+        cmake -S . -B build17
         -DPYBIND11_WERROR=ON
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
         -DCMAKE_CXX_STANDARD=17
-        ${{ matrix.args }}
-        ${{ matrix.args2 }}
 
-    - name: Build
-      run: cmake --build build2 -j 2
+    - name: Build C++17
+      run: cmake --build build17 -j 2
 
-    - name: Python tests
-      run: cmake --build build2 --target pytest
+    - name: Python tests C++17
+      run: cmake --build build17 --target pytest
 
-    - name: C++ tests
-      run: cmake --build build2 --target cpptest
+    - name: C++17 tests
+      run: cmake --build build17 --target cpptest
 
     # Third build - C++17 mode with unstable ABI
     - name: Configure (unstable ABI)
       run: >
-        cmake -S . -B build3
+        cmake -S . -B build17max
         -DPYBIND11_WERROR=ON
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
         -DCMAKE_CXX_STANDARD=17
         -DPYBIND11_INTERNALS_VERSION=10000000
-        "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
-        ${{ matrix.args }}
 
     - name: Build (unstable ABI)
-      run: cmake --build build3 -j 2
+      run: cmake --build build17max -j 2
 
     - name: Python tests (unstable ABI)
-      run: cmake --build build3 --target pytest
+      run: cmake --build build17max --target pytest
 
-    - name: Interface test
-      run: cmake --build build2 --target test_cmake_build
+    - name: Interface test (unstable ABI)
+      run: cmake --build build17max --target test_cmake_build
 
     # This makes sure the setup_helpers module can build packages using
     # setuptools
     - name: Setuptools helpers test
-      run: pytest tests/extra_setuptools
+      run: |
+        pip install setuptools
+        pytest tests/extra_setuptools
diff --git a/wrap/pybind11/.gitignore b/wrap/pybind11/.gitignore
index 3cf4fbbda..43d5094c9 100644
--- a/wrap/pybind11/.gitignore
+++ b/wrap/pybind11/.gitignore
@@ -43,3 +43,4 @@ pybind11Targets.cmake
 /pybind11/share/*
 /docs/_build/*
 .ipynb_checkpoints/
+tests/main.cpp
diff --git a/wrap/pybind11/.pre-commit-config.yaml b/wrap/pybind11/.pre-commit-config.yaml
index ba9955a31..86ac965d9 100644
--- a/wrap/pybind11/.pre-commit-config.yaml
+++ b/wrap/pybind11/.pre-commit-config.yaml
@@ -12,10 +12,62 @@
 #
 # See https://github.com/pre-commit/pre-commit
 
+
+ci:
+  autoupdate_commit_msg: "chore(deps): update pre-commit hooks"
+  autofix_commit_msg: "style: pre-commit fixes"
+  autoupdate_schedule: monthly
+
+# third-party content
+exclude: ^tools/JoinPaths.cmake$
+
 repos:
+
+# Clang format the codebase automatically
+- repo: https://github.com/pre-commit/mirrors-clang-format
+  rev: "v16.0.6"
+  hooks:
+  - id: clang-format
+    types_or: [c++, c, cuda]
+
+# Black, the code formatter, natively supports pre-commit
+- repo: https://github.com/psf/black
+  rev: "23.3.0" # Keep in sync with blacken-docs
+  hooks:
+  - id: black
+
+# Ruff, the Python auto-correcting linter written in Rust
+- repo: https://github.com/astral-sh/ruff-pre-commit
+  rev: v0.0.276
+  hooks:
+  - id: ruff
+    args: ["--fix", "--show-fixes"]
+
+# Check static types with mypy
+- repo: https://github.com/pre-commit/mirrors-mypy
+  rev: "v1.4.1"
+  hooks:
+  - id: mypy
+    args: []
+    exclude: ^(tests|docs)/
+    additional_dependencies:
+    - markdown-it-py<3 # Drop this together with dropping Python 3.7 support.
+    - nox
+    - rich
+    - types-setuptools
+
+# CMake formatting
+- repo: https://github.com/cheshirekow/cmake-format-precommit
+  rev: "v0.6.13"
+  hooks:
+  - id: cmake-format
+    additional_dependencies: [pyyaml]
+    types: [file]
+    files: (\.cmake|CMakeLists.txt)(.in)?$
+
 # Standard hooks
 - repo: https://github.com/pre-commit/pre-commit-hooks
-  rev: "v4.3.0"
+  rev: "v4.4.0"
   hooks:
   - id: check-added-large-files
   - id: check-case-conflict
@@ -30,109 +82,38 @@ repos:
   - id: requirements-txt-fixer
   - id: trailing-whitespace
 
-# Upgrade old Python syntax
-- repo: https://github.com/asottile/pyupgrade
-  rev: "v2.37.1"
-  hooks:
-  - id: pyupgrade
-    args: [--py36-plus]
-
-# Nicely sort includes
-- repo: https://github.com/PyCQA/isort
-  rev: "5.10.1"
-  hooks:
-  - id: isort
-
-# Black, the code formatter, natively supports pre-commit
-- repo: https://github.com/psf/black
-  rev: "22.6.0" # Keep in sync with blacken-docs
-  hooks:
-  - id: black
-
 # Also code format the docs
 - repo: https://github.com/asottile/blacken-docs
-  rev: "v1.12.1"
+  rev: "1.14.0"
   hooks:
   - id: blacken-docs
     additional_dependencies:
-    - black==22.6.0 # keep in sync with black hook
+    - black==23.3.0 # keep in sync with black hook
 
 # Changes tabs to spaces
 - repo: https://github.com/Lucas-C/pre-commit-hooks
-  rev: "v1.3.0"
+  rev: "v1.5.1"
   hooks:
   - id: remove-tabs
 
+# Avoid directional quotes
 - repo: https://github.com/sirosen/texthooks
-  rev: "0.3.1"
+  rev: "0.5.0"
   hooks:
   - id: fix-ligatures
   - id: fix-smartquotes
 
-# Autoremoves unused imports
-- repo: https://github.com/hadialqattan/pycln
-  rev: "v2.0.1"
-  hooks:
-  - id: pycln
-    stages: [manual]
-
 # Checking for common mistakes
 - repo: https://github.com/pre-commit/pygrep-hooks
-  rev: "v1.9.0"
+  rev: "v1.10.0"
   hooks:
-  - id: python-check-blanket-noqa
-  - id: python-check-blanket-type-ignore
-  - id: python-no-log-warn
-  - id: python-use-type-annotations
   - id: rst-backticks
   - id: rst-directive-colons
   - id: rst-inline-touching-normal
 
-# Automatically remove noqa that are not used
-- repo: https://github.com/asottile/yesqa
-  rev: "v1.3.0"
-  hooks:
-  - id: yesqa
-    additional_dependencies: &flake8_dependencies
-      - flake8-bugbear
-      - pep8-naming
-
-# Flake8 also supports pre-commit natively (same author)
-- repo: https://github.com/PyCQA/flake8
-  rev: "4.0.1"
-  hooks:
-  - id: flake8
-    exclude: ^(docs/.*|tools/.*)$
-    additional_dependencies: *flake8_dependencies
-
-# PyLint has native support - not always usable, but works for us
-- repo: https://github.com/PyCQA/pylint
-  rev: "v2.14.4"
-  hooks:
-  - id: pylint
-    files: ^pybind11
-
-# CMake formatting
-- repo: https://github.com/cheshirekow/cmake-format-precommit
-  rev: "v0.6.13"
-  hooks:
-  - id: cmake-format
-    additional_dependencies: [pyyaml]
-    types: [file]
-    files: (\.cmake|CMakeLists.txt)(.in)?$
-
-# Check static types with mypy
-- repo: https://github.com/pre-commit/mirrors-mypy
-  rev: "v0.961"
-  hooks:
-  - id: mypy
-    args: []
-    exclude: ^(tests|docs)/
-    additional_dependencies: [nox, rich]
-
 # Checks the manifest for missing files (native support)
 - repo: https://github.com/mgedmin/check-manifest
-  rev: "0.48"
+  rev: "0.49"
   hooks:
   - id: check-manifest
     # This is a slow hook, so only run this if --hook-stage manual is passed
@@ -140,16 +121,18 @@ repos:
     additional_dependencies: [cmake, ninja]
 
 # Check for spelling
+# Use tools/codespell_ignore_lines_from_errors.py
+# to rebuild .codespell-ignore-lines
 - repo: https://github.com/codespell-project/codespell
-  rev: "v2.1.0"
+  rev: "v2.2.5"
   hooks:
   - id: codespell
     exclude: ".supp$"
-    args: ["-L", "nd,ot,thist"]
+    args: ["-x.codespell-ignore-lines", "-Lccompiler"]
 
 # Check for common shell mistakes
 - repo: https://github.com/shellcheck-py/shellcheck-py
-  rev: "v0.8.0.4"
+  rev: "v0.9.0.5"
   hooks:
   - id: shellcheck
 
@@ -162,9 +145,9 @@ repos:
     entry: PyBind|Numpy|Cmake|CCache|PyTest
     exclude: ^\.pre-commit-config.yaml$
 
-# Clang format the codebase automatically
-- repo: https://github.com/pre-commit/mirrors-clang-format
-  rev: "v14.0.6"
+# PyLint has native support - not always usable, but works for us
+- repo: https://github.com/PyCQA/pylint
+  rev: "v3.0.0a6"
   hooks:
-  - id: clang-format
-    types_or: [c++, c, cuda]
+  - id: pylint
+    files: ^pybind11
diff --git a/wrap/pybind11/CMakeLists.txt b/wrap/pybind11/CMakeLists.txt
index 3787982cb..87ec10346 100644
--- a/wrap/pybind11/CMakeLists.txt
+++ b/wrap/pybind11/CMakeLists.txt
@@ -5,15 +5,15 @@
 # All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
-cmake_minimum_required(VERSION 3.4)
+cmake_minimum_required(VERSION 3.5)
 
-# The `cmake_minimum_required(VERSION 3.4...3.22)` syntax does not work with
+# The `cmake_minimum_required(VERSION 3.5...3.26)` syntax does not work with
 # some versions of VS that have a patched CMake 3.11. This forces us to emulate
 # the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.22)
+if(${CMAKE_VERSION} VERSION_LESS 3.26)
   cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
-  cmake_policy(VERSION 3.22)
+  cmake_policy(VERSION 3.26)
 endif()
 
 # Avoid infinite recursion if tests include this as a subdirectory
@@ -91,10 +91,16 @@ endif()
 option(PYBIND11_INSTALL "Install pybind11 header files?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_TEST "Build pybind11 test suite?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_NOPYTHON "Disable search for Python" OFF)
+option(PYBIND11_SIMPLE_GIL_MANAGEMENT
+       "Use simpler GIL management logic that does not support disassociation" OFF)
 set(PYBIND11_INTERNALS_VERSION
     ""
     CACHE STRING "Override the ABI version, may be used to enable the unstable ABI.")
 
+if(PYBIND11_SIMPLE_GIL_MANAGEMENT)
+  add_compile_definitions(PYBIND11_SIMPLE_GIL_MANAGEMENT)
+endif()
+
 cmake_dependent_option(
   USE_PYTHON_INCLUDE_DIR
   "Install pybind11 headers in Python include directory instead of default installation prefix"
@@ -120,6 +126,9 @@ set(PYBIND11_HEADERS
     include/pybind11/complex.h
     include/pybind11/options.h
     include/pybind11/eigen.h
+    include/pybind11/eigen/common.h
+    include/pybind11/eigen/matrix.h
+    include/pybind11/eigen/tensor.h
     include/pybind11/embed.h
     include/pybind11/eval.h
     include/pybind11/gil.h
@@ -131,7 +140,8 @@ set(PYBIND11_HEADERS
     include/pybind11/pytypes.h
     include/pybind11/stl.h
     include/pybind11/stl_bind.h
-    include/pybind11/stl/filesystem.h)
+    include/pybind11/stl/filesystem.h
+    include/pybind11/type_caster_pyobject_ptr.h)
 
 # Compare with grep and warn if mismatched
 if(PYBIND11_MASTER_PROJECT AND NOT CMAKE_VERSION VERSION_LESS 3.12)
@@ -198,6 +208,9 @@ else()
 endif()
 
 include("${CMAKE_CURRENT_SOURCE_DIR}/tools/pybind11Common.cmake")
+# https://github.com/jtojnar/cmake-snips/#concatenating-paths-when-building-pkg-config-files
+# TODO: cmake 3.20 adds the cmake_path() function, which obsoletes this snippet
+include("${CMAKE_CURRENT_SOURCE_DIR}/tools/JoinPaths.cmake")
 
 # Relative directory setting
 if(USE_PYTHON_INCLUDE_DIR AND DEFINED Python_INCLUDE_DIRS)
@@ -262,6 +275,16 @@ if(PYBIND11_INSTALL)
     NAMESPACE "pybind11::"
     DESTINATION ${PYBIND11_CMAKECONFIG_INSTALL_DIR})
 
+  # pkg-config support
+  if(NOT prefix_for_pc_file)
+    set(prefix_for_pc_file "${CMAKE_INSTALL_PREFIX}")
+  endif()
+  join_paths(includedir_for_pc_file "\${prefix}" "${CMAKE_INSTALL_INCLUDEDIR}")
+  configure_file("${CMAKE_CURRENT_SOURCE_DIR}/tools/pybind11.pc.in"
+                 "${CMAKE_CURRENT_BINARY_DIR}/pybind11.pc" @ONLY)
+  install(FILES "${CMAKE_CURRENT_BINARY_DIR}/pybind11.pc"
+          DESTINATION "${CMAKE_INSTALL_DATAROOTDIR}/pkgconfig/")
+
   # Uninstall target
   if(PYBIND11_MASTER_PROJECT)
     configure_file("${CMAKE_CURRENT_SOURCE_DIR}/tools/cmake_uninstall.cmake.in"
diff --git a/wrap/pybind11/MANIFEST.in b/wrap/pybind11/MANIFEST.in
index 033303a74..7ce83c552 100644
--- a/wrap/pybind11/MANIFEST.in
+++ b/wrap/pybind11/MANIFEST.in
@@ -1,5 +1,6 @@
+prune tests
 recursive-include pybind11/include/pybind11 *.h
 recursive-include pybind11 *.py
 recursive-include pybind11 py.typed
 include pybind11/share/cmake/pybind11/*.cmake
-include LICENSE README.rst pyproject.toml setup.py setup.cfg
+include LICENSE README.rst SECURITY.md pyproject.toml setup.py setup.cfg
diff --git a/wrap/pybind11/README.rst b/wrap/pybind11/README.rst
index 3c75edb57..80213a406 100644
--- a/wrap/pybind11/README.rst
+++ b/wrap/pybind11/README.rst
@@ -135,7 +135,7 @@ This project was created by `Wenzel
 Jakob <http://rgl.epfl.ch/people/wjakob>`_. Significant features and/or
 improvements to the code were contributed by Jonas Adler, Lori A. Burns,
 Sylvain Corlay, Eric Cousineau, Aaron Gokaslan, Ralf Grosse-Kunstleve, Trent Houliston, Axel
-Huebl, @hulucc, Yannick Jadoul, Sergey Lyskov Johan Mabille, Tomasz Miąsko,
+Huebl, @hulucc, Yannick Jadoul, Sergey Lyskov, Johan Mabille, Tomasz Miąsko,
 Dean Moldovan, Ben Pritchard, Jason Rhinelander, Boris Schäling, Pim
 Schellart, Henry Schreiner, Ivan Smirnov, Boris Staletic, and Patrick Stewart.
 
diff --git a/wrap/pybind11/SECURITY.md b/wrap/pybind11/SECURITY.md
new file mode 100644
index 000000000..3d74611f2
--- /dev/null
+++ b/wrap/pybind11/SECURITY.md
@@ -0,0 +1,13 @@
+# Security Policy
+
+## Supported Versions
+
+Security updates are applied only to the latest release.
+
+## Reporting a Vulnerability
+
+If you have discovered a security vulnerability in this project, please report it privately. **Do not disclose it as a public issue.** This gives us time to work with you to fix the issue before public exposure, reducing the chance that the exploit will be used before a patch is released.
+
+Please disclose it at [security advisory](https://github.com/pybind/pybind11/security/advisories/new).
+
+This project is maintained by a team of volunteers on a reasonable-effort basis. As such, please give us at least 90 days to work on a fix before public exposure.
diff --git a/wrap/pybind11/docs/advanced/cast/custom.rst b/wrap/pybind11/docs/advanced/cast/custom.rst
index 1df4d3e14..8138cac61 100644
--- a/wrap/pybind11/docs/advanced/cast/custom.rst
+++ b/wrap/pybind11/docs/advanced/cast/custom.rst
@@ -38,7 +38,7 @@ type is explicitly allowed.
 
 .. code-block:: cpp
 
-    namespace pybind11 { namespace detail {
+    namespace PYBIND11_NAMESPACE { namespace detail {
         template <> struct type_caster<inty> {
         public:
             /**
@@ -78,7 +78,7 @@ type is explicitly allowed.
                 return PyLong_FromLong(src.long_value);
             }
         };
-    }} // namespace pybind11::detail
+    }} // namespace PYBIND11_NAMESPACE::detail
 
 .. note::
 
diff --git a/wrap/pybind11/docs/advanced/cast/stl.rst b/wrap/pybind11/docs/advanced/cast/stl.rst
index 109763f7a..03d49b295 100644
--- a/wrap/pybind11/docs/advanced/cast/stl.rst
+++ b/wrap/pybind11/docs/advanced/cast/stl.rst
@@ -42,7 +42,7 @@ types:
 .. code-block:: cpp
 
     // `boost::optional` as an example -- can be any `std::optional`-like container
-    namespace pybind11 { namespace detail {
+    namespace PYBIND11_NAMESPACE { namespace detail {
         template <typename T>
         struct type_caster<boost::optional<T>> : optional_caster<boost::optional<T>> {};
     }}
@@ -54,7 +54,7 @@ for custom variant types:
 .. code-block:: cpp
 
     // `boost::variant` as an example -- can be any `std::variant`-like container
-    namespace pybind11 { namespace detail {
+    namespace PYBIND11_NAMESPACE { namespace detail {
         template <typename... Ts>
         struct type_caster<boost::variant<Ts...>> : variant_caster<boost::variant<Ts...>> {};
 
@@ -66,7 +66,7 @@ for custom variant types:
                 return boost::apply_visitor(args...);
             }
         };
-    }} // namespace pybind11::detail
+    }} // namespace PYBIND11_NAMESPACE::detail
 
 The ``visit_helper`` specialization is not required if your ``name::variant`` provides
 a ``name::visit()`` function. For any other function name, the specialization must be
diff --git a/wrap/pybind11/docs/advanced/cast/strings.rst b/wrap/pybind11/docs/advanced/cast/strings.rst
index e246c5219..271716b4b 100644
--- a/wrap/pybind11/docs/advanced/cast/strings.rst
+++ b/wrap/pybind11/docs/advanced/cast/strings.rst
@@ -101,8 +101,11 @@ conversion has the same overhead as implicit conversion.
     m.def("str_output",
         []() {
             std::string s = "Send your r\xe9sum\xe9 to Alice in HR"; // Latin-1
-            py::str py_s = PyUnicode_DecodeLatin1(s.data(), s.length());
-            return py_s;
+            py::handle py_s = PyUnicode_DecodeLatin1(s.data(), s.length(), nullptr);
+            if (!py_s) {
+                throw py::error_already_set();
+            }
+            return py::reinterpret_steal<py::str>(py_s);
         }
     );
 
@@ -113,7 +116,8 @@ conversion has the same overhead as implicit conversion.
 
 The `Python C API
 <https://docs.python.org/3/c-api/unicode.html#built-in-codecs>`_ provides
-several built-in codecs.
+several built-in codecs. Note that these all return *new* references, so
+use :cpp:func:`reinterpret_steal` when converting them to a :cpp:class:`str`.
 
 
 One could also use a third party encoding library such as libiconv to transcode
diff --git a/wrap/pybind11/docs/advanced/classes.rst b/wrap/pybind11/docs/advanced/classes.rst
index 49ddf5c0b..01a490b72 100644
--- a/wrap/pybind11/docs/advanced/classes.rst
+++ b/wrap/pybind11/docs/advanced/classes.rst
@@ -1228,7 +1228,7 @@ whether a downcast is safe, you can proceed by specializing the
         std::string bark() const { return sound; }
     };
 
-    namespace pybind11 {
+    namespace PYBIND11_NAMESPACE {
         template<> struct polymorphic_type_hook<Pet> {
             static const void *get(const Pet *src, const std::type_info*& type) {
                 // note that src may be nullptr
@@ -1239,7 +1239,7 @@ whether a downcast is safe, you can proceed by specializing the
                 return src;
             }
         };
-    } // namespace pybind11
+    } // namespace PYBIND11_NAMESPACE
 
 When pybind11 wants to convert a C++ pointer of type ``Base*`` to a
 Python object, it calls ``polymorphic_type_hook<Base>::get()`` to
diff --git a/wrap/pybind11/docs/advanced/embedding.rst b/wrap/pybind11/docs/advanced/embedding.rst
index dd980d483..e6a1686f8 100644
--- a/wrap/pybind11/docs/advanced/embedding.rst
+++ b/wrap/pybind11/docs/advanced/embedding.rst
@@ -18,7 +18,7 @@ information, see :doc:`/compiling`.
 
 .. code-block:: cmake
 
-    cmake_minimum_required(VERSION 3.4)
+    cmake_minimum_required(VERSION 3.5...3.26)
     project(example)
 
     find_package(pybind11 REQUIRED)  # or `add_subdirectory(pybind11)`
diff --git a/wrap/pybind11/docs/advanced/exceptions.rst b/wrap/pybind11/docs/advanced/exceptions.rst
index 2211caf5d..53981dc08 100644
--- a/wrap/pybind11/docs/advanced/exceptions.rst
+++ b/wrap/pybind11/docs/advanced/exceptions.rst
@@ -177,9 +177,12 @@ section.
     may be explicitly (re-)thrown to delegate it to the other,
     previously-declared existing exception translators.
 
-    Note that ``libc++`` and ``libstdc++`` `behave differently <https://stackoverflow.com/questions/19496643/using-clang-fvisibility-hidden-and-typeinfo-and-type-erasure/28827430>`_
-    with ``-fvisibility=hidden``. Therefore exceptions that are used across ABI boundaries need to be explicitly exported, as exercised in ``tests/test_exceptions.h``.
-    See also: "Problems with C++ exceptions" under `GCC Wiki <https://gcc.gnu.org/wiki/Visibility>`_.
+    Note that ``libc++`` and ``libstdc++`` `behave differently under macOS
+    <https://stackoverflow.com/questions/19496643/using-clang-fvisibility-hidden-and-typeinfo-and-type-erasure/28827430>`_
+    with ``-fvisibility=hidden``. Therefore exceptions that are used across ABI
+    boundaries need to be explicitly exported, as exercised in
+    ``tests/test_exceptions.h``. See also:
+    "Problems with C++ exceptions" under `GCC Wiki <https://gcc.gnu.org/wiki/Visibility>`_.
 
 
 Local vs Global Exception Translators
diff --git a/wrap/pybind11/docs/advanced/misc.rst b/wrap/pybind11/docs/advanced/misc.rst
index edab15fcb..805ec838f 100644
--- a/wrap/pybind11/docs/advanced/misc.rst
+++ b/wrap/pybind11/docs/advanced/misc.rst
@@ -39,15 +39,42 @@ The ``PYBIND11_MAKE_OPAQUE`` macro does *not* require the above workarounds.
 Global Interpreter Lock (GIL)
 =============================
 
-When calling a C++ function from Python, the GIL is always held.
+The Python C API dictates that the Global Interpreter Lock (GIL) must always
+be held by the current thread to safely access Python objects. As a result,
+when Python calls into C++ via pybind11 the GIL must be held, and pybind11
+will never implicitly release the GIL.
+
+.. code-block:: cpp
+
+    void my_function() {
+        /* GIL is held when this function is called from Python */
+    }
+
+    PYBIND11_MODULE(example, m) {
+        m.def("my_function", &my_function);
+    }
+
+pybind11 will ensure that the GIL is held when it knows that it is calling
+Python code. For example, if a Python callback is passed to C++ code via
+``std::function``, when C++ code calls the function the built-in wrapper
+will acquire the GIL before calling the Python callback. Similarly, the
+``PYBIND11_OVERRIDE`` family of macros will acquire the GIL before calling
+back into Python.
+
+When writing C++ code that is called from other C++ code, if that code accesses
+Python state, it must explicitly acquire and release the GIL.
+
 The classes :class:`gil_scoped_release` and :class:`gil_scoped_acquire` can be
 used to acquire and release the global interpreter lock in the body of a C++
 function call. In this way, long-running C++ code can be parallelized using
-multiple Python threads. Taking :ref:`overriding_virtuals` as an example, this
+multiple Python threads, **but great care must be taken** when any
+:class:`gil_scoped_release` appear: if there is any way that the C++ code
+can access Python objects, :class:`gil_scoped_acquire` should be used to
+reacquire the GIL. Taking :ref:`overriding_virtuals` as an example, this
 could be realized as follows (important changes highlighted):
 
 .. code-block:: cpp
-    :emphasize-lines: 8,9,31,32
+    :emphasize-lines: 8,30,31
 
     class PyAnimal : public Animal {
     public:
@@ -56,9 +83,7 @@ could be realized as follows (important changes highlighted):
 
         /* Trampoline (need one for each virtual function) */
         std::string go(int n_times) {
-            /* Acquire GIL before calling Python code */
-            py::gil_scoped_acquire acquire;
-
+            /* PYBIND11_OVERRIDE_PURE will acquire the GIL before accessing Python state */
             PYBIND11_OVERRIDE_PURE(
                 std::string, /* Return type */
                 Animal,      /* Parent class */
@@ -78,7 +103,8 @@ could be realized as follows (important changes highlighted):
             .def(py::init<>());
 
         m.def("call_go", [](Animal *animal) -> std::string {
-            /* Release GIL before calling into (potentially long-running) C++ code */
+            // GIL is held when called from Python code. Release GIL before
+            // calling into (potentially long-running) C++ code
             py::gil_scoped_release release;
             return call_go(animal);
         });
@@ -92,6 +118,34 @@ The ``call_go`` wrapper can also be simplified using the ``call_guard`` policy
     m.def("call_go", &call_go, py::call_guard<py::gil_scoped_release>());
 
 
+Common Sources Of Global Interpreter Lock Errors
+==================================================================
+
+Failing to properly hold the Global Interpreter Lock (GIL) is one of the
+more common sources of bugs within code that uses pybind11. If you are
+running into GIL related errors, we highly recommend you consult the
+following checklist.
+
+- Do you have any global variables that are pybind11 objects or invoke
+  pybind11 functions in either their constructor or destructor? You are generally
+  not allowed to invoke any Python function in a global static context. We recommend
+  using lazy initialization and then intentionally leaking at the end of the program.
+
+- Do you have any pybind11 objects that are members of other C++ structures? One
+  commonly overlooked requirement is that pybind11 objects have to increase their reference count
+  whenever their copy constructor is called. Thus, you need to be holding the GIL to invoke
+  the copy constructor of any C++ class that has a pybind11 member. This can sometimes be very
+  tricky to track for complicated programs Think carefully when you make a pybind11 object
+  a member in another struct.
+
+- C++ destructors that invoke Python functions can be particularly troublesome as
+  destructors can sometimes get invoked in weird and unexpected circumstances as a result
+  of exceptions.
+
+- You should try running your code in a debug build. That will enable additional assertions
+  within pybind11 that will throw exceptions on certain GIL handling errors
+  (reference counting operations).
+
 Binding sequence data types, iterators, the slicing protocol, etc.
 ==================================================================
 
@@ -298,6 +352,15 @@ The class ``options`` allows you to selectively suppress auto-generated signatur
         m.def("add", [](int a, int b) { return a + b; }, "A function which adds two numbers");
     }
 
+pybind11 also appends all members of an enum to the resulting enum docstring.
+This default behavior can be disabled by using the ``disable_enum_members_docstring()``
+function of the ``options`` class.
+
+With ``disable_user_defined_docstrings()`` all user defined docstrings of
+``module_::def()``, ``class_::def()`` and ``enum_()`` are disabled, but the
+function signatures and enum members are included in the docstring, unless they
+are disabled separately.
+
 Note that changes to the settings affect only function bindings created during the
 lifetime of the ``options`` instance. When it goes out of scope at the end of the module's init function,
 the default settings are restored to prevent unwanted side effects.
diff --git a/wrap/pybind11/docs/advanced/pycpp/numpy.rst b/wrap/pybind11/docs/advanced/pycpp/numpy.rst
index b6ef019ed..07c969305 100644
--- a/wrap/pybind11/docs/advanced/pycpp/numpy.rst
+++ b/wrap/pybind11/docs/advanced/pycpp/numpy.rst
@@ -433,7 +433,7 @@ following:
             { 2, 4 },                                  // shape (rows, cols)
             { sizeof(uint8_t) * 4, sizeof(uint8_t) }   // strides in bytes
         );
-    })
+    });
 
 This approach is meant for providing a ``memoryview`` for a C/C++ buffer not
 managed by Python. The user is responsible for managing the lifetime of the
@@ -449,7 +449,7 @@ We can also use ``memoryview::from_memory`` for a simple 1D contiguous buffer:
             buffer,               // buffer pointer
             sizeof(uint8_t) * 8   // buffer size
         );
-    })
+    });
 
 .. versionchanged:: 2.6
     ``memoryview::from_memory`` added.
diff --git a/wrap/pybind11/docs/advanced/smart_ptrs.rst b/wrap/pybind11/docs/advanced/smart_ptrs.rst
index 5a2220109..3c40ce123 100644
--- a/wrap/pybind11/docs/advanced/smart_ptrs.rst
+++ b/wrap/pybind11/docs/advanced/smart_ptrs.rst
@@ -157,7 +157,7 @@ specialized:
     PYBIND11_DECLARE_HOLDER_TYPE(T, SmartPtr<T>);
 
     // Only needed if the type's `.get()` goes by another name
-    namespace pybind11 { namespace detail {
+    namespace PYBIND11_NAMESPACE { namespace detail {
         template <typename T>
         struct holder_helper<SmartPtr<T>> { // <-- specialization
             static const T *get(const SmartPtr<T> &p) { return p.getPointer(); }
diff --git a/wrap/pybind11/docs/changelog.rst b/wrap/pybind11/docs/changelog.rst
index b926b27af..add3fd66b 100644
--- a/wrap/pybind11/docs/changelog.rst
+++ b/wrap/pybind11/docs/changelog.rst
@@ -9,6 +9,364 @@ Starting with version 1.8.0, pybind11 releases use a `semantic versioning
 Changes will be added here periodically from the "Suggested changelog entry"
 block in pull request descriptions.
 
+
+Version 2.11.1 (July 17, 2023)
+-----------------------------
+
+Changes:
+
+* ``PYBIND11_NO_ASSERT_GIL_HELD_INCREF_DECREF`` is now provided as an option
+  for disabling the default-on ``PyGILState_Check()``'s in
+  ``pybind11::handle``'s ``inc_ref()`` & ``dec_ref()``.
+  `#4753 <https://github.com/pybind/pybind11/pull/4753>`_
+
+* ``PYBIND11_ASSERT_GIL_HELD_INCREF_DECREF`` was disabled for PyPy in general
+  (not just PyPy Windows).
+  `#4751 <https://github.com/pybind/pybind11/pull/4751>`_
+
+
+Version 2.11.0 (July 14, 2023)
+-----------------------------
+
+New features:
+
+* The newly added ``pybind11::detail::is_move_constructible`` trait can be
+  specialized for cases in which ``std::is_move_constructible`` does not work
+  as needed. This is very similar to the long-established
+  ``pybind11::detail::is_copy_constructible``.
+  `#4631 <https://github.com/pybind/pybind11/pull/4631>`_
+
+* Introduce ``recursive_container_traits``.
+  `#4623 <https://github.com/pybind/pybind11/pull/4623>`_
+
+* ``pybind11/type_caster_pyobject_ptr.h`` was added to support automatic
+  wrapping of APIs that make use of ``PyObject *``. This header needs to
+  included explicitly (i.e. it is not included implicitly
+  with ``pybind/pybind11.h``).
+  `#4601 <https://github.com/pybind/pybind11/pull/4601>`_
+
+* ``format_descriptor<>`` & ``npy_format_descriptor<>`` ``PyObject *``
+  specializations were added. The latter enables ``py::array_t<PyObject *>``
+  to/from-python conversions.
+  `#4674 <https://github.com/pybind/pybind11/pull/4674>`_
+
+* ``buffer_info`` gained an ``item_type_is_equivalent_to<T>()`` member
+  function.
+  `#4674 <https://github.com/pybind/pybind11/pull/4674>`_
+
+* The ``capsule`` API gained a user-friendly constructor
+  (``py::capsule(ptr, "name", dtor)``).
+  `#4720 <https://github.com/pybind/pybind11/pull/4720>`_
+
+Changes:
+
+* ``PyGILState_Check()``'s in ``pybind11::handle``'s ``inc_ref()`` &
+  ``dec_ref()`` are now enabled by default again.
+  `#4246 <https://github.com/pybind/pybind11/pull/4246>`_
+
+* ``py::initialize_interpreter()`` using ``PyConfig_InitPythonConfig()``
+  instead of ``PyConfig_InitIsolatedConfig()``, to obtain complete
+  ``sys.path``.
+  `#4473 <https://github.com/pybind/pybind11/pull/4473>`_
+
+* Cast errors now always include Python type information, even if
+  ``PYBIND11_DETAILED_ERROR_MESSAGES`` is not defined. This increases binary
+  sizes slightly (~1.5%) but the error messages are much more informative.
+  `#4463 <https://github.com/pybind/pybind11/pull/4463>`_
+
+* The docstring generation for the ``std::array``-list caster was fixed.
+  Previously, signatures included the size of the list in a non-standard,
+  non-spec compliant way. The new format conforms to PEP 593.
+  **Tooling for processing the docstrings may need to be updated accordingly.**
+  `#4679 <https://github.com/pybind/pybind11/pull/4679>`_
+
+* Setter return values (which are inaccessible for all practical purposes) are
+  no longer converted to Python (only to be discarded).
+  `#4621 <https://github.com/pybind/pybind11/pull/4621>`_
+
+* Allow lambda specified to function definition to be ``noexcept(true)``
+  in C++17.
+  `#4593 <https://github.com/pybind/pybind11/pull/4593>`_
+
+* Get rid of recursive template instantiations for concatenating type
+  signatures on C++17 and higher.
+  `#4587 <https://github.com/pybind/pybind11/pull/4587>`_
+
+* Compatibility with Python 3.12 (beta). Note that the minimum pybind11
+  ABI version for Python 3.12 is version 5. (The default ABI version
+  for Python versions up to and including 3.11 is still version 4.).
+  `#4570 <https://github.com/pybind/pybind11/pull/4570>`_
+
+* With ``PYBIND11_INTERNALS_VERSION 5`` (default for Python 3.12+), MSVC builds
+  use ``std::hash<std::type_index>`` and ``std::equal_to<std::type_index>``
+  instead of string-based type comparisons. This resolves issues when binding
+  types defined in the unnamed namespace.
+  `#4319 <https://github.com/pybind/pybind11/pull/4319>`_
+
+* Python exception ``__notes__`` (introduced with Python 3.11) are now added to
+  the ``error_already_set::what()`` output.
+  `#4678 <https://github.com/pybind/pybind11/pull/4678>`_
+
+Build system improvements:
+
+* CMake 3.27 support was added, CMake 3.4 support was dropped.
+  FindPython will be used if ``FindPythonInterp`` is not present.
+  `#4719 <https://github.com/pybind/pybind11/pull/4719>`_
+
+* Update clang-tidy to 15 in CI.
+  `#4387 <https://github.com/pybind/pybind11/pull/4387>`_
+
+* Moved the linting framework over to Ruff.
+  `#4483 <https://github.com/pybind/pybind11/pull/4483>`_
+
+* Skip ``lto`` checks and target generation when
+  ``CMAKE_INTERPROCEDURAL_OPTIMIZATION`` is defined.
+  `#4643 <https://github.com/pybind/pybind11/pull/4643>`_
+
+* No longer inject ``-stdlib=libc++``, not needed for modern Pythons
+  (macOS 10.9+).
+  `#4639 <https://github.com/pybind/pybind11/pull/4639>`_
+
+* PyPy 3.10 support was added, PyPy 3.7 support was dropped.
+  `#4728 <https://github.com/pybind/pybind11/pull/4728>`_
+
+* Testing with Python 3.12 beta releases was added.
+  `#4713 <https://github.com/pybind/pybind11/pull/4713>`_
+
+
+Version 2.10.4 (Mar 16, 2023)
+-----------------------------
+
+Changes:
+
+* ``python3 -m pybind11`` gained a ``--version`` option (prints the version and
+  exits).
+  `#4526 <https://github.com/pybind/pybind11/pull/4526>`_
+
+Bug Fixes:
+
+* Fix a warning when pydebug is enabled on Python 3.11.
+  `#4461 <https://github.com/pybind/pybind11/pull/4461>`_
+
+* Ensure ``gil_scoped_release`` RAII is non-copyable.
+  `#4490 <https://github.com/pybind/pybind11/pull/4490>`_
+
+* Ensure the tests dir does not show up with new versions of setuptools.
+  `#4510 <https://github.com/pybind/pybind11/pull/4510>`_
+
+* Better stacklevel for a warning in setuptools helpers.
+  `#4516 <https://github.com/pybind/pybind11/pull/4516>`_
+
+Version 2.10.3 (Jan 3, 2023)
+----------------------------
+
+Changes:
+
+* Temporarily made our GIL status assertions (added in 2.10.2) disabled by
+  default (re-enable manually by defining
+  ``PYBIND11_ASSERT_GIL_HELD_INCREF_DECREF``, will be enabled in 2.11).
+  `#4432 <https://github.com/pybind/pybind11/pull/4432>`_
+
+* Improved error messages when ``inc_ref``/``dec_ref`` are called with an
+  invalid GIL state.
+  `#4427 <https://github.com/pybind/pybind11/pull/4427>`_
+  `#4436 <https://github.com/pybind/pybind11/pull/4436>`_
+
+Bug Fixes:
+
+* Some minor touchups found by static analyzers.
+  `#4440 <https://github.com/pybind/pybind11/pull/4440>`_
+
+
+Version 2.10.2 (Dec 20, 2022)
+-----------------------------
+
+Changes:
+
+* ``scoped_interpreter`` constructor taking ``PyConfig``.
+  `#4330 <https://github.com/pybind/pybind11/pull/4330>`_
+
+* ``pybind11/eigen/tensor.h`` adds converters to and from ``Eigen::Tensor`` and
+  ``Eigen::TensorMap``.
+  `#4201 <https://github.com/pybind/pybind11/pull/4201>`_
+
+* ``PyGILState_Check()``'s  were integrated to ``pybind11::handle``
+  ``inc_ref()`` & ``dec_ref()``. The added GIL checks are guarded by
+  ``PYBIND11_ASSERT_GIL_HELD_INCREF_DECREF``, which is the default only if
+  ``NDEBUG`` is not defined. (Made non-default in 2.10.3, will be active in 2.11)
+  `#4246 <https://github.com/pybind/pybind11/pull/4246>`_
+
+* Add option for enable/disable enum members in docstring.
+  `#2768 <https://github.com/pybind/pybind11/pull/2768>`_
+
+* Fixed typing of ``KeysView``, ``ValuesView`` and ``ItemsView`` in ``bind_map``.
+  `#4353 <https://github.com/pybind/pybind11/pull/4353>`_
+
+Bug fixes:
+
+* Bug fix affecting only Python 3.6 under very specific, uncommon conditions:
+  move ``PyEval_InitThreads()`` call to the correct location.
+  `#4350 <https://github.com/pybind/pybind11/pull/4350>`_
+
+* Fix segfault bug when passing foreign native functions to functional.h.
+  `#4254 <https://github.com/pybind/pybind11/pull/4254>`_
+
+Build system improvements:
+
+* Support setting PYTHON_LIBRARIES manually for Windows ARM cross-compilation
+  (classic mode).
+  `#4406 <https://github.com/pybind/pybind11/pull/4406>`_
+
+* Extend IPO/LTO detection for ICX (a.k.a IntelLLVM) compiler.
+  `#4402 <https://github.com/pybind/pybind11/pull/4402>`_
+
+* Allow calling ``find_package(pybind11 CONFIG)`` multiple times from separate
+  directories in the same CMake project and properly link Python (new mode).
+  `#4401 <https://github.com/pybind/pybind11/pull/4401>`_
+
+* ``multiprocessing_set_spawn`` in pytest fixture for added safety.
+  `#4377 <https://github.com/pybind/pybind11/pull/4377>`_
+
+* Fixed a bug in two pybind11/tools cmake scripts causing "Unknown arguments specified" errors.
+  `#4327 <https://github.com/pybind/pybind11/pull/4327>`_
+
+
+
+Version 2.10.1 (Oct 31, 2022)
+-----------------------------
+
+This is the first version to fully support embedding the newly released Python 3.11.
+
+Changes:
+
+* Allow ``pybind11::capsule`` constructor to take null destructor pointers.
+  `#4221 <https://github.com/pybind/pybind11/pull/4221>`_
+
+* ``embed.h`` was changed so that ``PYTHONPATH`` is used also with Python 3.11
+  (established behavior).
+  `#4119 <https://github.com/pybind/pybind11/pull/4119>`_
+
+* A ``PYBIND11_SIMPLE_GIL_MANAGEMENT`` option was added (cmake, C++ define),
+  along with many additional tests in ``test_gil_scoped.py``. The option may be
+  useful to try when debugging GIL-related issues, to determine if the more
+  complex default implementation is or is not to blame. See #4216 for
+  background. WARNING: Please be careful to not create ODR violations when
+  using the option: everything that is linked together with mutual symbol
+  visibility needs to be rebuilt.
+  `#4216 <https://github.com/pybind/pybind11/pull/4216>`_
+
+* ``PYBIND11_EXPORT_EXCEPTION`` was made non-empty only under macOS. This makes
+  Linux builds safer, and enables the removal of warning suppression pragmas for
+  Windows.
+  `#4298 <https://github.com/pybind/pybind11/pull/4298>`_
+
+Bug fixes:
+
+* Fixed a bug where ``UnicodeDecodeError`` was not propagated from various
+  ``py::str`` ctors when decoding surrogate utf characters.
+  `#4294 <https://github.com/pybind/pybind11/pull/4294>`_
+
+* Revert perfect forwarding for ``make_iterator``. This broke at least one
+  valid use case. May revisit later.
+  `#4234 <https://github.com/pybind/pybind11/pull/4234>`_
+
+* Fix support for safe casts to ``void*`` (regression in 2.10.0).
+  `#4275 <https://github.com/pybind/pybind11/pull/4275>`_
+
+* Fix ``char8_t`` support (regression in 2.9).
+  `#4278 <https://github.com/pybind/pybind11/pull/4278>`_
+
+* Unicode surrogate character in Python exception message leads to process
+  termination in ``error_already_set::what()``.
+  `#4297 <https://github.com/pybind/pybind11/pull/4297>`_
+
+* Fix MSVC 2019 v.1924 & C++14 mode error for ``overload_cast``.
+  `#4188 <https://github.com/pybind/pybind11/pull/4188>`_
+
+* Make augmented assignment operators non-const for the object-api. Behavior
+  was previously broken for augmented assignment operators.
+  `#4065 <https://github.com/pybind/pybind11/pull/4065>`_
+
+* Add proper error checking to C++ bindings for Python list append and insert.
+  `#4208 <https://github.com/pybind/pybind11/pull/4208>`_
+
+* Work-around for Nvidia's CUDA nvcc compiler in versions 11.4.0 - 11.8.0.
+  `#4220 <https://github.com/pybind/pybind11/pull/4220>`_
+
+* A workaround for PyPy was added in the ``py::error_already_set``
+  implementation, related to PR `#1895 <https://github.com/pybind/pybind11/pull/1895>`_
+  released with v2.10.0.
+  `#4079 <https://github.com/pybind/pybind11/pull/4079>`_
+
+* Fixed compiler errors when C++23 ``std::forward_like`` is available.
+  `#4136 <https://github.com/pybind/pybind11/pull/4136>`_
+
+* Properly raise exceptions in contains methods (like when an object in unhashable).
+  `#4209 <https://github.com/pybind/pybind11/pull/4209>`_
+
+* Further improve another error in exception handling.
+  `#4232 <https://github.com/pybind/pybind11/pull/4232>`_
+
+* ``get_local_internals()`` was made compatible with
+  ``finalize_interpreter()``, fixing potential freezes during interpreter
+  finalization.
+  `#4192 <https://github.com/pybind/pybind11/pull/4192>`_
+
+Performance and style:
+
+* Reserve space in set and STL map casters if possible. This will prevent
+  unnecessary rehashing / resizing by knowing the number of keys ahead of time
+  for Python to C++ casting. This improvement will greatly speed up the casting
+  of large unordered maps and sets.
+  `#4194 <https://github.com/pybind/pybind11/pull/4194>`_
+
+* GIL RAII scopes are non-copyable to avoid potential bugs.
+  `#4183 <https://github.com/pybind/pybind11/pull/4183>`_
+
+* Explicitly default all relevant ctors for pytypes in the ``PYBIND11_OBJECT``
+  macros and enforce the clang-tidy checks ``modernize-use-equals-default`` in
+  macros as well.
+  `#4017 <https://github.com/pybind/pybind11/pull/4017>`_
+
+* Optimize iterator advancement in C++ bindings.
+  `#4237 <https://github.com/pybind/pybind11/pull/4237>`_
+
+* Use the modern ``PyObject_GenericGetDict`` and ``PyObject_GenericSetDict``
+  for handling dynamic attribute dictionaries.
+  `#4106 <https://github.com/pybind/pybind11/pull/4106>`_
+
+* Document that users should use ``PYBIND11_NAMESPACE`` instead of using ``pybind11`` when
+  opening namespaces. Using namespace declarations and namespace qualification
+  remain the same as ``pybind11``. This is done to ensure consistent symbol
+  visibility.
+  `#4098 <https://github.com/pybind/pybind11/pull/4098>`_
+
+* Mark ``detail::forward_like`` as constexpr.
+  `#4147 <https://github.com/pybind/pybind11/pull/4147>`_
+
+* Optimize unpacking_collector when processing ``arg_v`` arguments.
+  `#4219 <https://github.com/pybind/pybind11/pull/4219>`_
+
+* Optimize casting C++ object to ``None``.
+  `#4269 <https://github.com/pybind/pybind11/pull/4269>`_
+
+
+Build system improvements:
+
+* CMake: revert overwrite behavior, now opt-in with ``PYBIND11_PYTHONLIBS_OVERRWRITE OFF``.
+  `#4195 <https://github.com/pybind/pybind11/pull/4195>`_
+
+* Include a pkg-config file when installing pybind11, such as in the Python
+  package.
+  `#4077 <https://github.com/pybind/pybind11/pull/4077>`_
+
+* Avoid stripping debug symbols when ``CMAKE_BUILD_TYPE`` is set to ``DEBUG``
+  instead of ``Debug``.
+  `#4078 <https://github.com/pybind/pybind11/pull/4078>`_
+
+* Followup to `#3948 <https://github.com/pybind/pybind11/pull/3948>`_, fixing vcpkg again.
+  `#4123 <https://github.com/pybind/pybind11/pull/4123>`_
+
 Version 2.10.0 (Jul 15, 2022)
 -----------------------------
 
diff --git a/wrap/pybind11/docs/classes.rst b/wrap/pybind11/docs/classes.rst
index c0c53135b..4f2167dac 100644
--- a/wrap/pybind11/docs/classes.rst
+++ b/wrap/pybind11/docs/classes.rst
@@ -58,6 +58,16 @@ interactive Python session demonstrating this example is shown below:
     Static member functions can be bound in the same way using
     :func:`class_::def_static`.
 
+.. note::
+
+    Binding C++ types in unnamed namespaces (also known as anonymous namespaces)
+    works reliably on many platforms, but not all. The `XFAIL_CONDITION` in
+    tests/test_unnamed_namespace_a.py encodes the currently known conditions.
+    For background see `#4319 <https://github.com/pybind/pybind11/pull/4319>`_.
+    If portability is a concern, it is therefore not recommended to bind C++
+    types in unnamed namespaces. It will be safest to manually pick unique
+    namespace names.
+
 Keyword and default arguments
 =============================
 It is possible to specify keyword and default arguments using the syntax
@@ -539,3 +549,7 @@ The ``name`` property returns the name of the enum value as a unicode string.
            ...
 
     By default, these are omitted to conserve space.
+
+.. warning::
+
+    Contrary to Python customs, enum values from the wrappers should not be compared using ``is``, but with ``==`` (see `#1177 <https://github.com/pybind/pybind11/issues/1177>`_ for background).
diff --git a/wrap/pybind11/docs/compiling.rst b/wrap/pybind11/docs/compiling.rst
index 2b543be0b..1fd098bec 100644
--- a/wrap/pybind11/docs/compiling.rst
+++ b/wrap/pybind11/docs/compiling.rst
@@ -241,7 +241,7 @@ extension module can be created with just a few lines of code:
 
 .. code-block:: cmake
 
-    cmake_minimum_required(VERSION 3.4...3.18)
+    cmake_minimum_required(VERSION 3.5...3.26)
     project(example LANGUAGES CXX)
 
     add_subdirectory(pybind11)
@@ -261,6 +261,9 @@ PyPI integration, can be found in the [cmake_example]_  repository.
 .. versionchanged:: 2.6
    CMake 3.4+ is required.
 
+.. versionchanged:: 2.11
+   CMake 3.5+ is required.
+
 Further information can be found at :doc:`cmake/index`.
 
 pybind11_add_module
@@ -495,7 +498,7 @@ You can use these targets to build complex applications. For example, the
 
 .. code-block:: cmake
 
-    cmake_minimum_required(VERSION 3.4)
+    cmake_minimum_required(VERSION 3.5...3.26)
     project(example LANGUAGES CXX)
 
     find_package(pybind11 REQUIRED)  # or add_subdirectory(pybind11)
@@ -553,7 +556,7 @@ information about usage in C++, see :doc:`/advanced/embedding`.
 
 .. code-block:: cmake
 
-    cmake_minimum_required(VERSION 3.4...3.18)
+    cmake_minimum_required(VERSION 3.5...3.26)
     project(example LANGUAGES CXX)
 
     find_package(pybind11 REQUIRED)  # or add_subdirectory(pybind11)
diff --git a/wrap/pybind11/docs/conf.py b/wrap/pybind11/docs/conf.py
index 2da6773f4..6e24751e9 100644
--- a/wrap/pybind11/docs/conf.py
+++ b/wrap/pybind11/docs/conf.py
@@ -353,12 +353,11 @@ def prepare(app):
         f.write(contents)
 
 
-def clean_up(app, exception):
+def clean_up(app, exception):  # noqa: ARG001
     (DIR / "readme.rst").unlink()
 
 
 def setup(app):
-
     # Add hook for building doxygen xml when needed
     app.connect("builder-inited", generate_doxygen_xml)
 
diff --git a/wrap/pybind11/docs/faq.rst b/wrap/pybind11/docs/faq.rst
index 28498e7df..1eb00efad 100644
--- a/wrap/pybind11/docs/faq.rst
+++ b/wrap/pybind11/docs/faq.rst
@@ -284,7 +284,8 @@ There are three possible solutions:
    COMPONENTS Interpreter Development)`` on modern CMake (3.12+, 3.15+ better,
    3.18.2+ best). Pybind11 in these cases uses the new CMake FindPython instead
    of the old, deprecated search tools, and these modules are much better at
-   finding the correct Python.
+   finding the correct Python. If FindPythonLibs/Interp are not available
+   (CMake 3.27+), then this will be ignored and FindPython will be used.
 3. Set ``PYBIND11_NOPYTHON`` to ``TRUE``. Pybind11 will not search for Python.
    However, you will have to use the target-based system, and do more setup
    yourself, because it does not know about or include things that depend on
diff --git a/wrap/pybind11/docs/release.rst b/wrap/pybind11/docs/release.rst
index e761cdf7a..4950c3b88 100644
--- a/wrap/pybind11/docs/release.rst
+++ b/wrap/pybind11/docs/release.rst
@@ -33,10 +33,12 @@ If you don't have nox, you should either use ``pipx run nox`` instead, or use
     - Run ``nox -s tests_packaging`` to ensure this was done correctly.
     - Ensure that all the information in ``setup.cfg`` is up-to-date, like
       supported Python versions.
-    - Add release date in ``docs/changelog.rst``.
-          - Check to make sure
-            `needs-changelog <https://github.com/pybind/pybind11/pulls?q=is%3Apr+is%3Aclosed+label%3A%22needs+changelog%22>`_
-            issues are entered in the changelog (clear the label when done).
+    - Add release date in ``docs/changelog.rst`` and integrate the output of
+      ``nox -s make_changelog``.
+          - Note that the ``make_changelog`` command inspects
+            `needs changelog <https://github.com/pybind/pybind11/pulls?q=is%3Apr+is%3Aclosed+label%3A%22needs+changelog%22>`_.
+          - Manually clear the ``needs changelog`` labels using the GitHub web
+            interface (very easy: start by clicking the link above).
     - ``git add`` and ``git commit``, ``git push``. **Ensure CI passes**. (If it
       fails due to a known flake issue, either ignore or restart CI.)
 - Add a release branch if this is a new minor version, or update the existing release branch if it is a patch version
diff --git a/wrap/pybind11/docs/upgrade.rst b/wrap/pybind11/docs/upgrade.rst
index 6a9db2d08..b13d21f5e 100644
--- a/wrap/pybind11/docs/upgrade.rst
+++ b/wrap/pybind11/docs/upgrade.rst
@@ -8,6 +8,20 @@ to a new version. But it goes into more detail. This includes things like
 deprecated APIs and their replacements, build system changes, general code
 modernization and other useful information.
 
+.. _upgrade-guide-2.11:
+
+v2.11
+=====
+
+* The minimum version of CMake is now 3.5. A future version will likely move to
+  requiring something like CMake 3.15. Note that CMake 3.27 is removing the
+  long-deprecated support for ``FindPythonInterp`` if you set 3.27 as the
+  minimum or maximum supported version. To prepare for that future, CMake 3.15+
+  using ``FindPython`` or setting ``PYBIND11_FINDPYTHON`` is highly recommended,
+  otherwise pybind11 will automatically switch to using ``FindPython`` if
+  ``FindPythonInterp`` is not available.
+
+
 .. _upgrade-guide-2.9:
 
 v2.9
diff --git a/wrap/pybind11/include/pybind11/attr.h b/wrap/pybind11/include/pybind11/attr.h
index db7cd8eff..1044db94d 100644
--- a/wrap/pybind11/include/pybind11/attr.h
+++ b/wrap/pybind11/include/pybind11/attr.h
@@ -26,6 +26,9 @@ struct is_method {
     explicit is_method(const handle &c) : class_(c) {}
 };
 
+/// Annotation for setters
+struct is_setter {};
+
 /// Annotation for operators
 struct is_operator {};
 
@@ -188,8 +191,8 @@ struct argument_record {
 struct function_record {
     function_record()
         : is_constructor(false), is_new_style_constructor(false), is_stateless(false),
-          is_operator(false), is_method(false), has_args(false), has_kwargs(false),
-          prepend(false) {}
+          is_operator(false), is_method(false), is_setter(false), has_args(false),
+          has_kwargs(false), prepend(false) {}
 
     /// Function name
     char *name = nullptr; /* why no C++ strings? They generate heavier code.. */
@@ -230,6 +233,9 @@ struct function_record {
     /// True if this is a method
     bool is_method : 1;
 
+    /// True if this is a setter
+    bool is_setter : 1;
+
     /// True if the function has a '*args' argument
     bool has_args : 1;
 
@@ -399,7 +405,7 @@ struct process_attribute<doc> : process_attribute_default<doc> {
 template <>
 struct process_attribute<const char *> : process_attribute_default<const char *> {
     static void init(const char *d, function_record *r) { r->doc = const_cast<char *>(d); }
-    static void init(const char *d, type_record *r) { r->doc = const_cast<char *>(d); }
+    static void init(const char *d, type_record *r) { r->doc = d; }
 };
 template <>
 struct process_attribute<char *> : process_attribute<const char *> {};
@@ -426,6 +432,12 @@ struct process_attribute<is_method> : process_attribute_default<is_method> {
     }
 };
 
+/// Process an attribute which indicates that this function is a setter
+template <>
+struct process_attribute<is_setter> : process_attribute_default<is_setter> {
+    static void init(const is_setter &, function_record *r) { r->is_setter = true; }
+};
+
 /// Process an attribute which indicates the parent scope of a method
 template <>
 struct process_attribute<scope> : process_attribute_default<scope> {
diff --git a/wrap/pybind11/include/pybind11/buffer_info.h b/wrap/pybind11/include/pybind11/buffer_info.h
index 06120d556..b99ee8bef 100644
--- a/wrap/pybind11/include/pybind11/buffer_info.h
+++ b/wrap/pybind11/include/pybind11/buffer_info.h
@@ -37,6 +37,9 @@ inline std::vector<ssize_t> f_strides(const std::vector<ssize_t> &shape, ssize_t
     return strides;
 }
 
+template <typename T, typename SFINAE = void>
+struct compare_buffer_info;
+
 PYBIND11_NAMESPACE_END(detail)
 
 /// Information record describing a Python buffer object
@@ -150,6 +153,17 @@ struct buffer_info {
     Py_buffer *view() const { return m_view; }
     Py_buffer *&view() { return m_view; }
 
+    /* True if the buffer item type is equivalent to `T`. */
+    // To define "equivalent" by example:
+    // `buffer_info::item_type_is_equivalent_to<int>(b)` and
+    // `buffer_info::item_type_is_equivalent_to<long>(b)` may both be true
+    // on some platforms, but `int` and `unsigned` will never be equivalent.
+    // For the ground truth, please inspect `detail::compare_buffer_info<>`.
+    template <typename T>
+    bool item_type_is_equivalent_to() const {
+        return detail::compare_buffer_info<T>::compare(*this);
+    }
+
 private:
     struct private_ctr_tag {};
 
@@ -170,9 +184,10 @@ private:
 
 PYBIND11_NAMESPACE_BEGIN(detail)
 
-template <typename T, typename SFINAE = void>
+template <typename T, typename SFINAE>
 struct compare_buffer_info {
     static bool compare(const buffer_info &b) {
+        // NOLINTNEXTLINE(bugprone-sizeof-expression) Needed for `PyObject *`
         return b.format == format_descriptor<T>::format() && b.itemsize == (ssize_t) sizeof(T);
     }
 };
diff --git a/wrap/pybind11/include/pybind11/cast.h b/wrap/pybind11/include/pybind11/cast.h
index a0e32281b..db3934118 100644
--- a/wrap/pybind11/include/pybind11/cast.h
+++ b/wrap/pybind11/include/pybind11/cast.h
@@ -29,6 +29,9 @@
 #include <vector>
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
 PYBIND11_NAMESPACE_BEGIN(detail)
 
 template <typename type, typename SFINAE = void>
@@ -88,7 +91,8 @@ public:
     template <typename T_,                                                                        \
               ::pybind11::detail::enable_if_t<                                                    \
                   std::is_same<type, ::pybind11::detail::remove_cv_t<T_>>::value,                 \
-                  int> = 0>                                                                       \
+                  int>                                                                            \
+              = 0>                                                                                \
     static ::pybind11::handle cast(                                                               \
         T_ *src, ::pybind11::return_value_policy policy, ::pybind11::handle parent) {             \
         if (!src)                                                                                 \
@@ -248,7 +252,7 @@ public:
         return false;
     }
     static handle cast(T, return_value_policy /* policy */, handle /* parent */) {
-        return none().inc_ref();
+        return none().release();
     }
     PYBIND11_TYPE_CASTER(T, const_name("None"));
 };
@@ -291,7 +295,7 @@ public:
         if (ptr) {
             return capsule(ptr).release();
         }
-        return none().inc_ref();
+        return none().release();
     }
 
     template <typename T>
@@ -389,7 +393,7 @@ struct string_caster {
 
         // For UTF-8 we avoid the need for a temporary `bytes` object by using
         // `PyUnicode_AsUTF8AndSize`.
-        if (PYBIND11_SILENCE_MSVC_C4127(UTF_N == 8)) {
+        if (UTF_N == 8) {
             Py_ssize_t size = -1;
             const auto *buffer
                 = reinterpret_cast<const CharT *>(PyUnicode_AsUTF8AndSize(load_src.ptr(), &size));
@@ -416,7 +420,7 @@ struct string_caster {
             = reinterpret_cast<const CharT *>(PYBIND11_BYTES_AS_STRING(utfNbytes.ptr()));
         size_t length = (size_t) PYBIND11_BYTES_SIZE(utfNbytes.ptr()) / sizeof(CharT);
         // Skip BOM for UTF-16/32
-        if (PYBIND11_SILENCE_MSVC_C4127(UTF_N > 8)) {
+        if (UTF_N > 8) {
             buffer++;
             length--;
         }
@@ -537,7 +541,7 @@ public:
 
     static handle cast(const CharT *src, return_value_policy policy, handle parent) {
         if (src == nullptr) {
-            return pybind11::none().inc_ref();
+            return pybind11::none().release();
         }
         return StringCaster::cast(StringType(src), policy, parent);
     }
@@ -572,7 +576,7 @@ public:
         // figure out how long the first encoded character is in bytes to distinguish between these
         // two errors.  We also allow want to allow unicode characters U+0080 through U+00FF, as
         // those can fit into a single char value.
-        if (PYBIND11_SILENCE_MSVC_C4127(StringCaster::UTF_N == 8) && str_len > 1 && str_len <= 4) {
+        if (StringCaster::UTF_N == 8 && str_len > 1 && str_len <= 4) {
             auto v0 = static_cast<unsigned char>(value[0]);
             // low bits only: 0-127
             // 0b110xxxxx - start of 2-byte sequence
@@ -598,7 +602,7 @@ public:
         // UTF-16 is much easier: we can only have a surrogate pair for values above U+FFFF, thus a
         // surrogate pair with total length 2 instantly indicates a range error (but not a "your
         // string was too long" error).
-        else if (PYBIND11_SILENCE_MSVC_C4127(StringCaster::UTF_N == 16) && str_len == 2) {
+        else if (StringCaster::UTF_N == 16 && str_len == 2) {
             one_char = static_cast<CharT>(value[0]);
             if (one_char >= 0xD800 && one_char < 0xE000) {
                 throw value_error("Character code point not in range(0x10000)");
@@ -960,7 +964,7 @@ struct move_always<
     enable_if_t<
         all_of<move_is_plain_type<T>,
                negation<is_copy_constructible<T>>,
-               std::is_move_constructible<T>,
+               is_move_constructible<T>,
                std::is_same<decltype(std::declval<make_caster<T>>().operator T &()), T &>>::value>>
     : std::true_type {};
 template <typename T, typename SFINAE = void>
@@ -971,7 +975,7 @@ struct move_if_unreferenced<
     enable_if_t<
         all_of<move_is_plain_type<T>,
                negation<move_always<T>>,
-               std::is_move_constructible<T>,
+               is_move_constructible<T>,
                std::is_same<decltype(std::declval<make_caster<T>>().operator T &()), T &>>::value>>
     : std::true_type {};
 template <typename T>
@@ -1013,11 +1017,14 @@ type_caster<T, SFINAE> &load_type(type_caster<T, SFINAE> &conv, const handle &ha
                   "Internal error: type_caster should only be used for C++ types");
     if (!conv.load(handle, true)) {
 #if !defined(PYBIND11_DETAILED_ERROR_MESSAGES)
-        throw cast_error("Unable to cast Python instance to C++ type (#define "
-                         "PYBIND11_DETAILED_ERROR_MESSAGES or compile in debug mode for details)");
+        throw cast_error(
+            "Unable to cast Python instance of type "
+            + str(type::handle_of(handle)).cast<std::string>()
+            + " to C++ type '?' (#define "
+              "PYBIND11_DETAILED_ERROR_MESSAGES or compile in debug mode for details)");
 #else
         throw cast_error("Unable to cast Python instance of type "
-                         + (std::string) str(type::handle_of(handle)) + " to C++ type '"
+                         + str(type::handle_of(handle)).cast<std::string>() + " to C++ type '"
                          + type_id<T>() + "'");
 #endif
     }
@@ -1034,7 +1041,11 @@ make_caster<T> load_type(const handle &handle) {
 PYBIND11_NAMESPACE_END(detail)
 
 // pytype -> C++ type
-template <typename T, detail::enable_if_t<!detail::is_pyobject<T>::value, int> = 0>
+template <typename T,
+          detail::enable_if_t<!detail::is_pyobject<T>::value
+                                  && !detail::is_same_ignoring_cvref<T, PyObject *>::value,
+                              int>
+          = 0>
 T cast(const handle &handle) {
     using namespace detail;
     static_assert(!cast_is_temporary_value_reference<T>::value,
@@ -1048,6 +1059,34 @@ T cast(const handle &handle) {
     return T(reinterpret_borrow<object>(handle));
 }
 
+// Note that `cast<PyObject *>(obj)` increments the reference count of `obj`.
+// This is necessary for the case that `obj` is a temporary, and could
+// not possibly be different, given
+// 1. the established convention that the passed `handle` is borrowed, and
+// 2. we don't want to force all generic code using `cast<T>()` to special-case
+//    handling of `T` = `PyObject *` (to increment the reference count there).
+// It is the responsibility of the caller to ensure that the reference count
+// is decremented.
+template <typename T,
+          typename Handle,
+          detail::enable_if_t<detail::is_same_ignoring_cvref<T, PyObject *>::value
+                                  && detail::is_same_ignoring_cvref<Handle, handle>::value,
+                              int>
+          = 0>
+T cast(Handle &&handle) {
+    return handle.inc_ref().ptr();
+}
+// To optimize way an inc_ref/dec_ref cycle:
+template <typename T,
+          typename Object,
+          detail::enable_if_t<detail::is_same_ignoring_cvref<T, PyObject *>::value
+                                  && detail::is_same_ignoring_cvref<Object, object>::value,
+                              int>
+          = 0>
+T cast(Object &&obj) {
+    return obj.release().ptr();
+}
+
 // C++ type -> py::object
 template <typename T, detail::enable_if_t<!detail::is_pyobject<T>::value, int> = 0>
 object cast(T &&value,
@@ -1081,12 +1120,13 @@ detail::enable_if_t<!detail::move_never<T>::value, T> move(object &&obj) {
     if (obj.ref_count() > 1) {
 #if !defined(PYBIND11_DETAILED_ERROR_MESSAGES)
         throw cast_error(
-            "Unable to cast Python instance to C++ rvalue: instance has multiple references"
-            " (#define PYBIND11_DETAILED_ERROR_MESSAGES or compile in debug mode for details)");
+            "Unable to cast Python " + str(type::handle_of(obj)).cast<std::string>()
+            + " instance to C++ rvalue: instance has multiple references"
+              " (#define PYBIND11_DETAILED_ERROR_MESSAGES or compile in debug mode for details)");
 #else
-        throw cast_error("Unable to move from Python " + (std::string) str(type::handle_of(obj))
-                         + " instance to C++ " + type_id<T>()
-                         + " instance: instance has multiple references");
+        throw cast_error("Unable to move from Python "
+                         + str(type::handle_of(obj)).cast<std::string>() + " instance to C++ "
+                         + type_id<T>() + " instance: instance has multiple references");
 #endif
     }
 
@@ -1179,11 +1219,9 @@ enable_if_t<cast_is_temporary_value_reference<T>::value, T> cast_safe(object &&)
     pybind11_fail("Internal error: cast_safe fallback invoked");
 }
 template <typename T>
-enable_if_t<std::is_same<void, intrinsic_t<T>>::value, void> cast_safe(object &&) {}
+enable_if_t<std::is_void<T>::value, void> cast_safe(object &&) {}
 template <typename T>
-enable_if_t<detail::none_of<cast_is_temporary_value_reference<T>,
-                            std::is_same<void, intrinsic_t<T>>>::value,
-            T>
+enable_if_t<detail::none_of<cast_is_temporary_value_reference<T>, std::is_void<T>>::value, T>
 cast_safe(object &&o) {
     return pybind11::cast<T>(std::move(o));
 }
@@ -1193,9 +1231,10 @@ PYBIND11_NAMESPACE_END(detail)
 // The overloads could coexist, i.e. the #if is not strictly speaking needed,
 // but it is an easy minor optimization.
 #if !defined(PYBIND11_DETAILED_ERROR_MESSAGES)
-inline cast_error cast_error_unable_to_convert_call_arg() {
-    return cast_error("Unable to convert call argument to Python object (#define "
-                      "PYBIND11_DETAILED_ERROR_MESSAGES or compile in debug mode for details)");
+inline cast_error cast_error_unable_to_convert_call_arg(const std::string &name) {
+    return cast_error("Unable to convert call argument '" + name
+                      + "' to Python object (#define "
+                        "PYBIND11_DETAILED_ERROR_MESSAGES or compile in debug mode for details)");
 }
 #else
 inline cast_error cast_error_unable_to_convert_call_arg(const std::string &name,
@@ -1218,7 +1257,7 @@ tuple make_tuple(Args &&...args_) {
     for (size_t i = 0; i < args.size(); i++) {
         if (!args[i]) {
 #if !defined(PYBIND11_DETAILED_ERROR_MESSAGES)
-            throw cast_error_unable_to_convert_call_arg();
+            throw cast_error_unable_to_convert_call_arg(std::to_string(i));
 #else
             std::array<std::string, size> argtypes{{type_id<Args>()...}};
             throw cast_error_unable_to_convert_call_arg(std::to_string(i), argtypes[i]);
@@ -1508,7 +1547,7 @@ private:
             detail::make_caster<T>::cast(std::forward<T>(x), policy, {}));
         if (!o) {
 #if !defined(PYBIND11_DETAILED_ERROR_MESSAGES)
-            throw cast_error_unable_to_convert_call_arg();
+            throw cast_error_unable_to_convert_call_arg(std::to_string(args_list.size()));
 #else
             throw cast_error_unable_to_convert_call_arg(std::to_string(args_list.size()),
                                                         type_id<T>());
@@ -1540,12 +1579,12 @@ private:
         }
         if (!a.value) {
 #if !defined(PYBIND11_DETAILED_ERROR_MESSAGES)
-            throw cast_error_unable_to_convert_call_arg();
+            throw cast_error_unable_to_convert_call_arg(a.name);
 #else
             throw cast_error_unable_to_convert_call_arg(a.name, a.type);
 #endif
         }
-        m_kwargs[a.name] = a.value;
+        m_kwargs[a.name] = std::move(a.value);
     }
 
     void process(list & /*args_list*/, detail::kwargs_proxy kp) {
diff --git a/wrap/pybind11/include/pybind11/detail/class.h b/wrap/pybind11/include/pybind11/detail/class.h
index 42720f844..bc2b40c50 100644
--- a/wrap/pybind11/include/pybind11/detail/class.h
+++ b/wrap/pybind11/include/pybind11/detail/class.h
@@ -55,6 +55,9 @@ extern "C" inline int pybind11_static_set(PyObject *self, PyObject *obj, PyObjec
     return PyProperty_Type.tp_descr_set(self, cls, value);
 }
 
+// Forward declaration to use in `make_static_property_type()`
+inline void enable_dynamic_attributes(PyHeapTypeObject *heap_type);
+
 /** A `static_property` is the same as a `property` but the `__get__()` and `__set__()`
     methods are modified to always use the object type instead of a concrete instance.
     Return value: New reference. */
@@ -87,6 +90,13 @@ inline PyTypeObject *make_static_property_type() {
         pybind11_fail("make_static_property_type(): failure in PyType_Ready()!");
     }
 
+#    if PY_VERSION_HEX >= 0x030C0000
+    // PRE 3.12 FEATURE FREEZE. PLEASE REVIEW AFTER FREEZE.
+    // Since Python-3.12 property-derived types are required to
+    // have dynamic attributes (to set `__doc__`)
+    enable_dynamic_attributes(heap_type);
+#    endif
+
     setattr((PyObject *) type, "__module__", str("pybind11_builtins"));
     PYBIND11_SET_OLDPY_QUALNAME(type, name_obj);
 
@@ -435,9 +445,17 @@ inline void clear_instance(PyObject *self) {
 /// Instance destructor function for all pybind11 types. It calls `type_info.dealloc`
 /// to destroy the C++ object itself, while the rest is Python bookkeeping.
 extern "C" inline void pybind11_object_dealloc(PyObject *self) {
+    auto *type = Py_TYPE(self);
+
+    // If this is a GC tracked object, untrack it first
+    // Note that the track call is implicitly done by the
+    // default tp_alloc, which we never override.
+    if (PyType_HasFeature(type, Py_TPFLAGS_HAVE_GC) != 0) {
+        PyObject_GC_UnTrack(self);
+    }
+
     clear_instance(self);
 
-    auto *type = Py_TYPE(self);
     type->tp_free(self);
 
 #if PY_VERSION_HEX < 0x03080000
@@ -502,31 +520,6 @@ inline PyObject *make_object_base_type(PyTypeObject *metaclass) {
     return (PyObject *) heap_type;
 }
 
-/// dynamic_attr: Support for `d = instance.__dict__`.
-extern "C" inline PyObject *pybind11_get_dict(PyObject *self, void *) {
-    PyObject *&dict = *_PyObject_GetDictPtr(self);
-    if (!dict) {
-        dict = PyDict_New();
-    }
-    Py_XINCREF(dict);
-    return dict;
-}
-
-/// dynamic_attr: Support for `instance.__dict__ = dict()`.
-extern "C" inline int pybind11_set_dict(PyObject *self, PyObject *new_dict, void *) {
-    if (!PyDict_Check(new_dict)) {
-        PyErr_Format(PyExc_TypeError,
-                     "__dict__ must be set to a dictionary, not a '%.200s'",
-                     get_fully_qualified_tp_name(Py_TYPE(new_dict)).c_str());
-        return -1;
-    }
-    PyObject *&dict = *_PyObject_GetDictPtr(self);
-    Py_INCREF(new_dict);
-    Py_CLEAR(dict);
-    dict = new_dict;
-    return 0;
-}
-
 /// dynamic_attr: Allow the garbage collector to traverse the internal instance `__dict__`.
 extern "C" inline int pybind11_traverse(PyObject *self, visitproc visit, void *arg) {
     PyObject *&dict = *_PyObject_GetDictPtr(self);
@@ -558,9 +551,17 @@ inline void enable_dynamic_attributes(PyHeapTypeObject *heap_type) {
     type->tp_traverse = pybind11_traverse;
     type->tp_clear = pybind11_clear;
 
-    static PyGetSetDef getset[] = {
-        {const_cast<char *>("__dict__"), pybind11_get_dict, pybind11_set_dict, nullptr, nullptr},
-        {nullptr, nullptr, nullptr, nullptr, nullptr}};
+    static PyGetSetDef getset[] = {{
+#if PY_VERSION_HEX < 0x03070000
+                                       const_cast<char *>("__dict__"),
+#else
+                                       "__dict__",
+#endif
+                                       PyObject_GenericGetDict,
+                                       PyObject_GenericSetDict,
+                                       nullptr,
+                                       nullptr},
+                                   {nullptr, nullptr, nullptr, nullptr, nullptr}};
     type->tp_getset = getset;
 }
 
diff --git a/wrap/pybind11/include/pybind11/detail/common.h b/wrap/pybind11/include/pybind11/detail/common.h
index 1da323f31..31a54c773 100644
--- a/wrap/pybind11/include/pybind11/detail/common.h
+++ b/wrap/pybind11/include/pybind11/detail/common.h
@@ -10,15 +10,76 @@
 #pragma once
 
 #define PYBIND11_VERSION_MAJOR 2
-#define PYBIND11_VERSION_MINOR 10
-#define PYBIND11_VERSION_PATCH 0
+#define PYBIND11_VERSION_MINOR 11
+#define PYBIND11_VERSION_PATCH 1
 
 // Similar to Python's convention: https://docs.python.org/3/c-api/apiabiversion.html
 // Additional convention: 0xD = dev
-#define PYBIND11_VERSION_HEX 0x020A0000
+#define PYBIND11_VERSION_HEX 0x020B0100
 
-#define PYBIND11_NAMESPACE_BEGIN(name) namespace name {
-#define PYBIND11_NAMESPACE_END(name) }
+// Define some generic pybind11 helper macros for warning management.
+//
+// Note that compiler-specific push/pop pairs are baked into the
+// PYBIND11_NAMESPACE_BEGIN/PYBIND11_NAMESPACE_END pair of macros. Therefore manual
+// PYBIND11_WARNING_PUSH/PYBIND11_WARNING_POP are usually only needed in `#include` sections.
+//
+// If you find you need to suppress a warning, please try to make the suppression as local as
+// possible using these macros. Please also be sure to push/pop with the pybind11 macros. Please
+// only use compiler specifics if you need to check specific versions, e.g. Apple Clang vs. vanilla
+// Clang.
+#if defined(_MSC_VER)
+#    define PYBIND11_COMPILER_MSVC
+#    define PYBIND11_PRAGMA(...) __pragma(__VA_ARGS__)
+#    define PYBIND11_WARNING_PUSH PYBIND11_PRAGMA(warning(push))
+#    define PYBIND11_WARNING_POP PYBIND11_PRAGMA(warning(pop))
+#elif defined(__INTEL_COMPILER)
+#    define PYBIND11_COMPILER_INTEL
+#    define PYBIND11_PRAGMA(...) _Pragma(#__VA_ARGS__)
+#    define PYBIND11_WARNING_PUSH PYBIND11_PRAGMA(warning push)
+#    define PYBIND11_WARNING_POP PYBIND11_PRAGMA(warning pop)
+#elif defined(__clang__)
+#    define PYBIND11_COMPILER_CLANG
+#    define PYBIND11_PRAGMA(...) _Pragma(#__VA_ARGS__)
+#    define PYBIND11_WARNING_PUSH PYBIND11_PRAGMA(clang diagnostic push)
+#    define PYBIND11_WARNING_POP PYBIND11_PRAGMA(clang diagnostic push)
+#elif defined(__GNUC__)
+#    define PYBIND11_COMPILER_GCC
+#    define PYBIND11_PRAGMA(...) _Pragma(#__VA_ARGS__)
+#    define PYBIND11_WARNING_PUSH PYBIND11_PRAGMA(GCC diagnostic push)
+#    define PYBIND11_WARNING_POP PYBIND11_PRAGMA(GCC diagnostic pop)
+#endif
+
+#ifdef PYBIND11_COMPILER_MSVC
+#    define PYBIND11_WARNING_DISABLE_MSVC(name) PYBIND11_PRAGMA(warning(disable : name))
+#else
+#    define PYBIND11_WARNING_DISABLE_MSVC(name)
+#endif
+
+#ifdef PYBIND11_COMPILER_CLANG
+#    define PYBIND11_WARNING_DISABLE_CLANG(name) PYBIND11_PRAGMA(clang diagnostic ignored name)
+#else
+#    define PYBIND11_WARNING_DISABLE_CLANG(name)
+#endif
+
+#ifdef PYBIND11_COMPILER_GCC
+#    define PYBIND11_WARNING_DISABLE_GCC(name) PYBIND11_PRAGMA(GCC diagnostic ignored name)
+#else
+#    define PYBIND11_WARNING_DISABLE_GCC(name)
+#endif
+
+#ifdef PYBIND11_COMPILER_INTEL
+#    define PYBIND11_WARNING_DISABLE_INTEL(name) PYBIND11_PRAGMA(warning disable name)
+#else
+#    define PYBIND11_WARNING_DISABLE_INTEL(name)
+#endif
+
+#define PYBIND11_NAMESPACE_BEGIN(name)                                                            \
+    namespace name {                                                                              \
+    PYBIND11_WARNING_PUSH
+
+#define PYBIND11_NAMESPACE_END(name)                                                              \
+    PYBIND11_WARNING_POP                                                                          \
+    }
 
 // Robust support for some features and loading modules compiled against different pybind versions
 // requires forcing hidden visibility on pybind code, so we enforce this by setting the attribute
@@ -96,13 +157,10 @@
 #endif
 
 #if !defined(PYBIND11_EXPORT_EXCEPTION)
-#    ifdef __MINGW32__
-// workaround for:
-// error: 'dllexport' implies default visibility, but xxx has already been declared with a
-// different visibility
-#        define PYBIND11_EXPORT_EXCEPTION
-#    else
+#    if defined(__apple_build_version__)
 #        define PYBIND11_EXPORT_EXCEPTION PYBIND11_EXPORT
+#    else
+#        define PYBIND11_EXPORT_EXCEPTION
 #    endif
 #endif
 
@@ -154,9 +212,9 @@
 
 /// Include Python header, disable linking to pythonX_d.lib on Windows in debug mode
 #if defined(_MSC_VER)
-#    pragma warning(push)
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_MSVC(4505)
 // C4505: 'PySlice_GetIndicesEx': unreferenced local function has been removed (PyPy only)
-#    pragma warning(disable : 4505)
 #    if defined(_DEBUG) && !defined(Py_DEBUG)
 // Workaround for a VS 2022 issue.
 // NOTE: This workaround knowingly violates the Python.h include order requirement:
@@ -205,11 +263,8 @@
 #    endif
 #endif
 
-#if defined(__cpp_lib_char8_t) && __cpp_lib_char8_t >= 201811L
-#    define PYBIND11_HAS_U8STRING
-#endif
-
 #include <Python.h>
+// Reminder: WITH_THREAD is always defined if PY_VERSION_HEX >= 0x03070000
 #if PY_VERSION_HEX < 0x03060000
 #    error "PYTHON < 3.6 IS UNSUPPORTED. pybind11 v2.9 was the last to support Python 2 and 3.5."
 #endif
@@ -233,12 +288,16 @@
 #    undef copysign
 #endif
 
+#if defined(PYPY_VERSION) && !defined(PYBIND11_SIMPLE_GIL_MANAGEMENT)
+#    define PYBIND11_SIMPLE_GIL_MANAGEMENT
+#endif
+
 #if defined(_MSC_VER)
 #    if defined(PYBIND11_DEBUG_MARKER)
 #        define _DEBUG
 #        undef PYBIND11_DEBUG_MARKER
 #    endif
-#    pragma warning(pop)
+PYBIND11_WARNING_POP
 #endif
 
 #include <cstddef>
@@ -259,6 +318,17 @@
 #    endif
 #endif
 
+// Must be after including <version> or one of the other headers specified by the standard
+#if defined(__cpp_lib_char8_t) && __cpp_lib_char8_t >= 201811L
+#    define PYBIND11_HAS_U8STRING
+#endif
+
+// See description of PR #4246:
+#if !defined(PYBIND11_NO_ASSERT_GIL_HELD_INCREF_DECREF) && !defined(NDEBUG)                       \
+    && !defined(PYPY_VERSION) && !defined(PYBIND11_ASSERT_GIL_HELD_INCREF_DECREF)
+#    define PYBIND11_ASSERT_GIL_HELD_INCREF_DECREF
+#endif
+
 // #define PYBIND11_STR_LEGACY_PERMISSIVE
 // If DEFINED, pybind11::str can hold PyUnicodeObject or PyBytesObject
 //             (probably surprising and never documented, but this was the
@@ -363,7 +433,7 @@
 
 /** \rst
     This macro creates the entry point that will be invoked when the Python interpreter
-    imports an extension module. The module name is given as the fist argument and it
+    imports an extension module. The module name is given as the first argument and it
     should not be in quotes. The second macro argument defines a variable of type
     `py::module_` which can be used to initialize the module.
 
@@ -588,6 +658,10 @@ template <class T>
 using remove_cvref_t = typename remove_cvref<T>::type;
 #endif
 
+/// Example usage: is_same_ignoring_cvref<T, PyObject *>::value
+template <typename T, typename U>
+using is_same_ignoring_cvref = std::is_same<detail::remove_cvref_t<T>, U>;
+
 /// Index sequences
 #if defined(PYBIND11_CPP14)
 using std::index_sequence;
@@ -681,7 +755,16 @@ template <typename C, typename R, typename... A>
 struct remove_class<R (C::*)(A...) const> {
     using type = R(A...);
 };
-
+#ifdef __cpp_noexcept_function_type
+template <typename C, typename R, typename... A>
+struct remove_class<R (C::*)(A...) noexcept> {
+    using type = R(A...);
+};
+template <typename C, typename R, typename... A>
+struct remove_class<R (C::*)(A...) const noexcept> {
+    using type = R(A...);
+};
+#endif
 /// Helper template to strip away type modifiers
 template <typename T>
 struct intrinsic_type {
@@ -898,12 +981,6 @@ using expand_side_effects = bool[];
 
 PYBIND11_NAMESPACE_END(detail)
 
-#if defined(_MSC_VER)
-#    pragma warning(push)
-#    pragma warning(disable : 4275)
-//     warning C4275: An exported class was derived from a class that wasn't exported.
-//     Can be ignored when derived from a STL class.
-#endif
 /// C++ bindings of builtin Python exceptions
 class PYBIND11_EXPORT_EXCEPTION builtin_exception : public std::runtime_error {
 public:
@@ -911,9 +988,6 @@ public:
     /// Set the error using the Python C API
     virtual void set_error() const = 0;
 };
-#if defined(_MSC_VER)
-#    pragma warning(pop)
-#endif
 
 #define PYBIND11_RUNTIME_EXCEPTION(name, type)                                                    \
     class PYBIND11_EXPORT_EXCEPTION name : public builtin_exception {                             \
@@ -948,6 +1022,15 @@ PYBIND11_RUNTIME_EXCEPTION(reference_cast_error, PyExc_RuntimeError) /// Used in
 template <typename T, typename SFINAE = void>
 struct format_descriptor {};
 
+template <typename T>
+struct format_descriptor<
+    T,
+    detail::enable_if_t<detail::is_same_ignoring_cvref<T, PyObject *>::value>> {
+    static constexpr const char c = 'O';
+    static constexpr const char value[2] = {c, '\0'};
+    static std::string format() { return std::string(1, c); }
+};
+
 PYBIND11_NAMESPACE_BEGIN(detail)
 // Returns the index of the given type in the type char array below, and in the list in numpy.h
 // The order here is: bool; 8 ints ((signed,unsigned)x(8,16,32,64)bits); float,double,long double;
@@ -1033,12 +1116,7 @@ PYBIND11_NAMESPACE_END(detail)
 ///  - regular: static_cast<Return (Class::*)(Arg0, Arg1, Arg2)>(&Class::func)
 ///  - sweet:   overload_cast<Arg0, Arg1, Arg2>(&Class::func)
 template <typename... Args>
-#    if (defined(_MSC_VER) && _MSC_VER < 1920) /* MSVC 2017 */                                    \
-        || (defined(__clang__) && __clang_major__ == 5)
-static constexpr detail::overload_cast_impl<Args...> overload_cast = {};
-#    else
-static constexpr detail::overload_cast_impl<Args...> overload_cast;
-#    endif
+static constexpr detail::overload_cast_impl<Args...> overload_cast{};
 #endif
 
 /// Const member function selector for overload_cast
@@ -1147,20 +1225,28 @@ constexpr
 #    define PYBIND11_WORKAROUND_INCORRECT_GCC_UNUSED_BUT_SET_PARAMETER(...)
 #endif
 
-#if defined(_MSC_VER) // All versions (as of July 2021).
-
-// warning C4127: Conditional expression is constant
-constexpr inline bool silence_msvc_c4127(bool cond) { return cond; }
-
-#    define PYBIND11_SILENCE_MSVC_C4127(...) ::pybind11::detail::silence_msvc_c4127(__VA_ARGS__)
-
-#else
-#    define PYBIND11_SILENCE_MSVC_C4127(...) __VA_ARGS__
+#if defined(__clang__)                                                                            \
+    && (defined(__apple_build_version__) /* AppleClang 13.0.0.13000029 was the only data point    \
+                                            available. */                                         \
+        || (__clang_major__ >= 7                                                                  \
+            && __clang_major__ <= 12) /* Clang 3, 5, 13, 14, 15 do not generate the warning. */   \
+    )
+#    define PYBIND11_DETECTED_CLANG_WITH_MISLEADING_CALL_STD_MOVE_EXPLICITLY_WARNING
+// Example:
+// tests/test_kwargs_and_defaults.cpp:46:68: error: local variable 'args' will be copied despite
+// being returned by name [-Werror,-Wreturn-std-move]
+//     m.def("args_function", [](py::args args) -> py::tuple { return args; });
+//                                                                    ^~~~
+// test_kwargs_and_defaults.cpp:46:68: note: call 'std::move' explicitly to avoid copying
+//     m.def("args_function", [](py::args args) -> py::tuple { return args; });
+//                                                                    ^~~~
+//                                                                    std::move(args)
 #endif
 
 // Pybind offers detailed error messages by default for all builts that are debug (through the
-// negation of ndebug). This can also be manually enabled by users, for any builds, through
-// defining PYBIND11_DETAILED_ERROR_MESSAGES.
+// negation of NDEBUG). This can also be manually enabled by users, for any builds, through
+// defining PYBIND11_DETAILED_ERROR_MESSAGES. This information is primarily useful for those
+// who are writing (as opposed to merely using) libraries that use pybind11.
 #if !defined(PYBIND11_DETAILED_ERROR_MESSAGES) && !defined(NDEBUG)
 #    define PYBIND11_DETAILED_ERROR_MESSAGES
 #endif
diff --git a/wrap/pybind11/include/pybind11/detail/descr.h b/wrap/pybind11/include/pybind11/detail/descr.h
index e7a5e2c14..635614b0d 100644
--- a/wrap/pybind11/include/pybind11/detail/descr.h
+++ b/wrap/pybind11/include/pybind11/detail/descr.h
@@ -143,11 +143,24 @@ constexpr descr<N, Ts...> concat(const descr<N, Ts...> &descr) {
     return descr;
 }
 
+#ifdef __cpp_fold_expressions
+template <size_t N1, size_t N2, typename... Ts1, typename... Ts2>
+constexpr descr<N1 + N2 + 2, Ts1..., Ts2...> operator,(const descr<N1, Ts1...> &a,
+                                                       const descr<N2, Ts2...> &b) {
+    return a + const_name(", ") + b;
+}
+
+template <size_t N, typename... Ts, typename... Args>
+constexpr auto concat(const descr<N, Ts...> &d, const Args &...args) {
+    return (d, ..., args);
+}
+#else
 template <size_t N, typename... Ts, typename... Args>
 constexpr auto concat(const descr<N, Ts...> &d, const Args &...args)
     -> decltype(std::declval<descr<N + 2, Ts...>>() + concat(args...)) {
     return d + const_name(", ") + concat(args...);
 }
+#endif
 
 template <size_t N, typename... Ts>
 constexpr descr<N + 2, Ts...> type_descr(const descr<N, Ts...> &descr) {
diff --git a/wrap/pybind11/include/pybind11/detail/init.h b/wrap/pybind11/include/pybind11/detail/init.h
index 05f4fe54a..e21171688 100644
--- a/wrap/pybind11/include/pybind11/detail/init.h
+++ b/wrap/pybind11/include/pybind11/detail/init.h
@@ -12,6 +12,9 @@
 #include "class.h"
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
 PYBIND11_NAMESPACE_BEGIN(detail)
 
 template <>
@@ -115,7 +118,7 @@ template <typename Class>
 void construct(value_and_holder &v_h, Cpp<Class> *ptr, bool need_alias) {
     PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
     no_nullptr(ptr);
-    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr)) {
+    if (Class::has_alias && need_alias && !is_alias<Class>(ptr)) {
         // We're going to try to construct an alias by moving the cpp type.  Whether or not
         // that succeeds, we still need to destroy the original cpp pointer (either the
         // moved away leftover, if the alias construction works, or the value itself if we
@@ -156,7 +159,7 @@ void construct(value_and_holder &v_h, Holder<Class> holder, bool need_alias) {
     auto *ptr = holder_helper<Holder<Class>>::get(holder);
     no_nullptr(ptr);
     // If we need an alias, check that the held pointer is actually an alias instance
-    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr)) {
+    if (Class::has_alias && need_alias && !is_alias<Class>(ptr)) {
         throw type_error("pybind11::init(): construction failed: returned holder-wrapped instance "
                          "is not an alias instance");
     }
@@ -172,9 +175,9 @@ void construct(value_and_holder &v_h, Holder<Class> holder, bool need_alias) {
 template <typename Class>
 void construct(value_and_holder &v_h, Cpp<Class> &&result, bool need_alias) {
     PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
-    static_assert(std::is_move_constructible<Cpp<Class>>::value,
+    static_assert(is_move_constructible<Cpp<Class>>::value,
                   "pybind11::init() return-by-value factory function requires a movable class");
-    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias) {
+    if (Class::has_alias && need_alias) {
         construct_alias_from_cpp<Class>(is_alias_constructible<Class>{}, v_h, std::move(result));
     } else {
         v_h.value_ptr() = new Cpp<Class>(std::move(result));
@@ -187,7 +190,7 @@ void construct(value_and_holder &v_h, Cpp<Class> &&result, bool need_alias) {
 template <typename Class>
 void construct(value_and_holder &v_h, Alias<Class> &&result, bool) {
     static_assert(
-        std::is_move_constructible<Alias<Class>>::value,
+        is_move_constructible<Alias<Class>>::value,
         "pybind11::init() return-by-alias-value factory function requires a movable alias class");
     v_h.value_ptr() = new Alias<Class>(std::move(result));
 }
@@ -206,10 +209,11 @@ struct constructor {
             extra...);
     }
 
-    template <typename Class,
-              typename... Extra,
-              enable_if_t<Class::has_alias && std::is_constructible<Cpp<Class>, Args...>::value,
-                          int> = 0>
+    template <
+        typename Class,
+        typename... Extra,
+        enable_if_t<Class::has_alias && std::is_constructible<Cpp<Class>, Args...>::value, int>
+        = 0>
     static void execute(Class &cl, const Extra &...extra) {
         cl.def(
             "__init__",
@@ -226,10 +230,11 @@ struct constructor {
             extra...);
     }
 
-    template <typename Class,
-              typename... Extra,
-              enable_if_t<Class::has_alias && !std::is_constructible<Cpp<Class>, Args...>::value,
-                          int> = 0>
+    template <
+        typename Class,
+        typename... Extra,
+        enable_if_t<Class::has_alias && !std::is_constructible<Cpp<Class>, Args...>::value, int>
+        = 0>
     static void execute(Class &cl, const Extra &...extra) {
         cl.def(
             "__init__",
@@ -245,10 +250,11 @@ struct constructor {
 // Implementing class for py::init_alias<...>()
 template <typename... Args>
 struct alias_constructor {
-    template <typename Class,
-              typename... Extra,
-              enable_if_t<Class::has_alias && std::is_constructible<Alias<Class>, Args...>::value,
-                          int> = 0>
+    template <
+        typename Class,
+        typename... Extra,
+        enable_if_t<Class::has_alias && std::is_constructible<Alias<Class>, Args...>::value, int>
+        = 0>
     static void execute(Class &cl, const Extra &...extra) {
         cl.def(
             "__init__",
diff --git a/wrap/pybind11/include/pybind11/detail/internals.h b/wrap/pybind11/include/pybind11/detail/internals.h
index 6ca5e1482..aaa7f8686 100644
--- a/wrap/pybind11/include/pybind11/detail/internals.h
+++ b/wrap/pybind11/include/pybind11/detail/internals.h
@@ -9,6 +9,12 @@
 
 #pragma once
 
+#include "common.h"
+
+#if defined(WITH_THREAD) && defined(PYBIND11_SIMPLE_GIL_MANAGEMENT)
+#    include "../gil.h"
+#endif
+
 #include "../pytypes.h"
 
 #include <exception>
@@ -28,15 +34,26 @@
 /// further ABI-incompatible changes may be made before the ABI is officially
 /// changed to the new version.
 #ifndef PYBIND11_INTERNALS_VERSION
-#    define PYBIND11_INTERNALS_VERSION 4
+#    if PY_VERSION_HEX >= 0x030C0000
+// Version bump for Python 3.12+, before first 3.12 beta release.
+#        define PYBIND11_INTERNALS_VERSION 5
+#    else
+#        define PYBIND11_INTERNALS_VERSION 4
+#    endif
 #endif
 
+// This requirement is mainly to reduce the support burden (see PR #4570).
+static_assert(PY_VERSION_HEX < 0x030C0000 || PYBIND11_INTERNALS_VERSION >= 5,
+              "pybind11 ABI version 5 is the minimum for Python 3.12+");
+
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
 using ExceptionTranslator = void (*)(std::exception_ptr);
 
 PYBIND11_NAMESPACE_BEGIN(detail)
 
+constexpr const char *internals_function_record_capsule_name = "pybind11_function_record_capsule";
+
 // Forward declarations
 inline PyTypeObject *make_static_property_type();
 inline PyTypeObject *make_default_metaclass();
@@ -49,7 +66,7 @@ inline PyObject *make_object_base_type(PyTypeObject *metaclass);
 // `Py_LIMITED_API` anyway.
 #    if PYBIND11_INTERNALS_VERSION > 4
 #        define PYBIND11_TLS_KEY_REF Py_tss_t &
-#        ifdef __GNUC__
+#        if defined(__GNUC__) && !defined(__INTEL_COMPILER)
 // Clang on macOS warns due to `Py_tss_NEEDS_INIT` not specifying an initializer
 // for every field.
 #            define PYBIND11_TLS_KEY_INIT(var)                                                    \
@@ -106,7 +123,8 @@ inline void tls_replace_value(PYBIND11_TLS_KEY_REF key, void *value) {
 // libstdc++, this doesn't happen: equality and the type_index hash are based on the type name,
 // which works.  If not under a known-good stl, provide our own name-based hash and equality
 // functions that use the type name.
-#if defined(__GLIBCXX__)
+#if (PYBIND11_INTERNALS_VERSION <= 4 && defined(__GLIBCXX__))                                     \
+    || (PYBIND11_INTERNALS_VERSION >= 5 && !defined(_LIBCPP_VERSION))
 inline bool same_type(const std::type_info &lhs, const std::type_info &rhs) { return lhs == rhs; }
 using type_hash = std::hash<std::type_index>;
 using type_equal_to = std::equal_to<std::type_index>;
@@ -169,11 +187,23 @@ struct internals {
     PyTypeObject *default_metaclass;
     PyObject *instance_base;
 #if defined(WITH_THREAD)
+    // Unused if PYBIND11_SIMPLE_GIL_MANAGEMENT is defined:
     PYBIND11_TLS_KEY_INIT(tstate)
 #    if PYBIND11_INTERNALS_VERSION > 4
     PYBIND11_TLS_KEY_INIT(loader_life_support_tls_key)
 #    endif // PYBIND11_INTERNALS_VERSION > 4
+    // Unused if PYBIND11_SIMPLE_GIL_MANAGEMENT is defined:
     PyInterpreterState *istate = nullptr;
+
+#    if PYBIND11_INTERNALS_VERSION > 4
+    // Note that we have to use a std::string to allocate memory to ensure a unique address
+    // We want unique addresses since we use pointer equality to compare function records
+    std::string function_record_capsule_name = internals_function_record_capsule_name;
+#    endif
+
+    internals() = default;
+    internals(const internals &other) = delete;
+    internals &operator=(const internals &other) = delete;
     ~internals() {
 #    if PYBIND11_INTERNALS_VERSION > 4
         PYBIND11_TLS_FREE(loader_life_support_tls_key);
@@ -401,6 +431,38 @@ inline void translate_local_exception(std::exception_ptr p) {
 }
 #endif
 
+inline object get_python_state_dict() {
+    object state_dict;
+#if PYBIND11_INTERNALS_VERSION <= 4 || PY_VERSION_HEX < 0x03080000 || defined(PYPY_VERSION)
+    state_dict = reinterpret_borrow<object>(PyEval_GetBuiltins());
+#else
+#    if PY_VERSION_HEX < 0x03090000
+    PyInterpreterState *istate = _PyInterpreterState_Get();
+#    else
+    PyInterpreterState *istate = PyInterpreterState_Get();
+#    endif
+    if (istate) {
+        state_dict = reinterpret_borrow<object>(PyInterpreterState_GetDict(istate));
+    }
+#endif
+    if (!state_dict) {
+        raise_from(PyExc_SystemError, "pybind11::detail::get_python_state_dict() FAILED");
+    }
+    return state_dict;
+}
+
+inline object get_internals_obj_from_state_dict(handle state_dict) {
+    return reinterpret_borrow<object>(dict_getitemstring(state_dict.ptr(), PYBIND11_INTERNALS_ID));
+}
+
+inline internals **get_internals_pp_from_capsule(handle obj) {
+    void *raw_ptr = PyCapsule_GetPointer(obj.ptr(), /*name=*/nullptr);
+    if (raw_ptr == nullptr) {
+        raise_from(PyExc_SystemError, "pybind11::detail::get_internals_pp_from_capsule() FAILED");
+    }
+    return static_cast<internals **>(raw_ptr);
+}
+
 /// Return a reference to the current `internals` data
 PYBIND11_NOINLINE internals &get_internals() {
     auto **&internals_pp = get_internals_pp();
@@ -408,21 +470,29 @@ PYBIND11_NOINLINE internals &get_internals() {
         return **internals_pp;
     }
 
+#if defined(WITH_THREAD)
+#    if defined(PYBIND11_SIMPLE_GIL_MANAGEMENT)
+    gil_scoped_acquire gil;
+#    else
     // Ensure that the GIL is held since we will need to make Python calls.
     // Cannot use py::gil_scoped_acquire here since that constructor calls get_internals.
     struct gil_scoped_acquire_local {
         gil_scoped_acquire_local() : state(PyGILState_Ensure()) {}
+        gil_scoped_acquire_local(const gil_scoped_acquire_local &) = delete;
+        gil_scoped_acquire_local &operator=(const gil_scoped_acquire_local &) = delete;
         ~gil_scoped_acquire_local() { PyGILState_Release(state); }
         const PyGILState_STATE state;
     } gil;
+#    endif
+#endif
     error_scope err_scope;
 
-    PYBIND11_STR_TYPE id(PYBIND11_INTERNALS_ID);
-    auto builtins = handle(PyEval_GetBuiltins());
-    if (builtins.contains(id) && isinstance<capsule>(builtins[id])) {
-        internals_pp = static_cast<internals **>(capsule(builtins[id]));
-
-        // We loaded builtins through python's builtins, which means that our `error_already_set`
+    dict state_dict = get_python_state_dict();
+    if (object internals_obj = get_internals_obj_from_state_dict(state_dict)) {
+        internals_pp = get_internals_pp_from_capsule(internals_obj);
+    }
+    if (internals_pp && *internals_pp) {
+        // We loaded the internals through `state_dict`, which means that our `error_already_set`
         // and `builtin_exception` may be different local classes than the ones set up in the
         // initial exception translator, below, so add another for our local exception classes.
         //
@@ -440,16 +510,15 @@ PYBIND11_NOINLINE internals &get_internals() {
         internals_ptr = new internals();
 #if defined(WITH_THREAD)
 
-#    if PY_VERSION_HEX < 0x03090000
-        PyEval_InitThreads();
-#    endif
         PyThreadState *tstate = PyThreadState_Get();
+        // NOLINTNEXTLINE(bugprone-assignment-in-if-condition)
         if (!PYBIND11_TLS_KEY_CREATE(internals_ptr->tstate)) {
             pybind11_fail("get_internals: could not successfully initialize the tstate TSS key!");
         }
         PYBIND11_TLS_REPLACE_VALUE(internals_ptr->tstate, tstate);
 
 #    if PYBIND11_INTERNALS_VERSION > 4
+        // NOLINTNEXTLINE(bugprone-assignment-in-if-condition)
         if (!PYBIND11_TLS_KEY_CREATE(internals_ptr->loader_life_support_tls_key)) {
             pybind11_fail("get_internals: could not successfully initialize the "
                           "loader_life_support TSS key!");
@@ -457,7 +526,7 @@ PYBIND11_NOINLINE internals &get_internals() {
 #    endif
         internals_ptr->istate = tstate->interp;
 #endif
-        builtins[id] = capsule(internals_pp);
+        state_dict[PYBIND11_INTERNALS_ID] = capsule(internals_pp);
         internals_ptr->registered_exception_translators.push_front(&translate_exception);
         internals_ptr->static_property_type = make_static_property_type();
         internals_ptr->default_metaclass = make_default_metaclass();
@@ -489,6 +558,7 @@ struct local_internals {
     struct shared_loader_life_support_data {
         PYBIND11_TLS_KEY_INIT(loader_life_support_tls_key)
         shared_loader_life_support_data() {
+            // NOLINTNEXTLINE(bugprone-assignment-in-if-condition)
             if (!PYBIND11_TLS_KEY_CREATE(loader_life_support_tls_key)) {
                 pybind11_fail("local_internals: could not successfully initialize the "
                               "loader_life_support TLS key!");
@@ -512,8 +582,13 @@ struct local_internals {
 
 /// Works like `get_internals`, but for things which are locally registered.
 inline local_internals &get_local_internals() {
-    static local_internals locals;
-    return locals;
+    // Current static can be created in the interpreter finalization routine. If the later will be
+    // destroyed in another static variable destructor, creation of this static there will cause
+    // static deinitialization fiasco. In order to avoid it we avoid destruction of the
+    // local_internals static. One can read more about the problem and current solution here:
+    // https://google.github.io/styleguide/cppguide.html#Static_and_Global_Variables
+    static auto *locals = new local_internals();
+    return *locals;
 }
 
 /// Constructs a std::string with the given arguments, stores it in `internals`, and returns its
@@ -527,6 +602,25 @@ const char *c_str(Args &&...args) {
     return strings.front().c_str();
 }
 
+inline const char *get_function_record_capsule_name() {
+#if PYBIND11_INTERNALS_VERSION > 4
+    return get_internals().function_record_capsule_name.c_str();
+#else
+    return nullptr;
+#endif
+}
+
+// Determine whether or not the following capsule contains a pybind11 function record.
+// Note that we use `internals` to make sure that only ABI compatible records are touched.
+//
+// This check is currently used in two places:
+// - An important optimization in functional.h to avoid overhead in C++ -> Python -> C++
+// - The sibling feature of cpp_function to allow overloads
+inline bool is_function_record_capsule(const capsule &cap) {
+    // Pointer equality as we rely on internals() to ensure unique pointers
+    return cap.name() == get_function_record_capsule_name();
+}
+
 PYBIND11_NAMESPACE_END(detail)
 
 /// Returns a named pointer that is shared among all extension modules (using the same
diff --git a/wrap/pybind11/include/pybind11/detail/type_caster_base.h b/wrap/pybind11/include/pybind11/detail/type_caster_base.h
index 21f69c289..16387506c 100644
--- a/wrap/pybind11/include/pybind11/detail/type_caster_base.h
+++ b/wrap/pybind11/include/pybind11/detail/type_caster_base.h
@@ -258,9 +258,9 @@ struct value_and_holder {
 
     // Main constructor for a found value/holder:
     value_and_holder(instance *i, const detail::type_info *type, size_t vpos, size_t index)
-        : inst{i}, index{index}, type{type}, vh{inst->simple_layout
-                                                    ? inst->simple_value_holder
-                                                    : &inst->nonsimple.values_and_holders[vpos]} {}
+        : inst{i}, index{index}, type{type},
+          vh{inst->simple_layout ? inst->simple_value_holder
+                                 : &inst->nonsimple.values_and_holders[vpos]} {}
 
     // Default constructor (used to signal a value-and-holder not found by get_value_and_holder())
     value_and_holder() = default;
@@ -822,23 +822,179 @@ using movable_cast_op_type
                                   typename std::add_rvalue_reference<intrinsic_t<T>>::type,
                                   typename std::add_lvalue_reference<intrinsic_t<T>>::type>>;
 
+// Does the container have a mapped type and is it recursive?
+// Implemented by specializations below.
+template <typename Container, typename SFINAE = void>
+struct container_mapped_type_traits {
+    static constexpr bool has_mapped_type = false;
+    static constexpr bool has_recursive_mapped_type = false;
+};
+
+template <typename Container>
+struct container_mapped_type_traits<
+    Container,
+    typename std::enable_if<
+        std::is_same<typename Container::mapped_type, Container>::value>::type> {
+    static constexpr bool has_mapped_type = true;
+    static constexpr bool has_recursive_mapped_type = true;
+};
+
+template <typename Container>
+struct container_mapped_type_traits<
+    Container,
+    typename std::enable_if<
+        negation<std::is_same<typename Container::mapped_type, Container>>::value>::type> {
+    static constexpr bool has_mapped_type = true;
+    static constexpr bool has_recursive_mapped_type = false;
+};
+
+// Does the container have a value type and is it recursive?
+// Implemented by specializations below.
+template <typename Container, typename SFINAE = void>
+struct container_value_type_traits : std::false_type {
+    static constexpr bool has_value_type = false;
+    static constexpr bool has_recursive_value_type = false;
+};
+
+template <typename Container>
+struct container_value_type_traits<
+    Container,
+    typename std::enable_if<
+        std::is_same<typename Container::value_type, Container>::value>::type> {
+    static constexpr bool has_value_type = true;
+    static constexpr bool has_recursive_value_type = true;
+};
+
+template <typename Container>
+struct container_value_type_traits<
+    Container,
+    typename std::enable_if<
+        negation<std::is_same<typename Container::value_type, Container>>::value>::type> {
+    static constexpr bool has_value_type = true;
+    static constexpr bool has_recursive_value_type = false;
+};
+
+/*
+ * Tag to be used for representing the bottom of recursively defined types.
+ * Define this tag so we don't have to use void.
+ */
+struct recursive_bottom {};
+
+/*
+ * Implementation detail of `recursive_container_traits` below.
+ * `T` is the `value_type` of the container, which might need to be modified to
+ * avoid recursive types and const types.
+ */
+template <typename T, bool is_this_a_map>
+struct impl_type_to_check_recursively {
+    /*
+     * If the container is recursive, then no further recursion should be done.
+     */
+    using if_recursive = recursive_bottom;
+    /*
+     * Otherwise yield `T` unchanged.
+     */
+    using if_not_recursive = T;
+};
+
+/*
+ * For pairs - only as value type of a map -, the first type should remove the `const`.
+ * Also, if the map is recursive, then the recursive checking should consider
+ * the first type only.
+ */
+template <typename A, typename B>
+struct impl_type_to_check_recursively<std::pair<A, B>, /* is_this_a_map = */ true> {
+    using if_recursive = typename std::remove_const<A>::type;
+    using if_not_recursive = std::pair<typename std::remove_const<A>::type, B>;
+};
+
+/*
+ * Implementation of `recursive_container_traits` below.
+ */
+template <typename Container, typename SFINAE = void>
+struct impl_recursive_container_traits {
+    using type_to_check_recursively = recursive_bottom;
+};
+
+template <typename Container>
+struct impl_recursive_container_traits<
+    Container,
+    typename std::enable_if<container_value_type_traits<Container>::has_value_type>::type> {
+    static constexpr bool is_recursive
+        = container_mapped_type_traits<Container>::has_recursive_mapped_type
+          || container_value_type_traits<Container>::has_recursive_value_type;
+    /*
+     * This member dictates which type Pybind11 should check recursively in traits
+     * such as `is_move_constructible`, `is_copy_constructible`, `is_move_assignable`, ...
+     * Direct access to `value_type` should be avoided:
+     * 1. `value_type` might recursively contain the type again
+     * 2. `value_type` of STL map types is `std::pair<A const, B>`, the `const`
+     *    should be removed.
+     *
+     */
+    using type_to_check_recursively = typename std::conditional<
+        is_recursive,
+        typename impl_type_to_check_recursively<
+            typename Container::value_type,
+            container_mapped_type_traits<Container>::has_mapped_type>::if_recursive,
+        typename impl_type_to_check_recursively<
+            typename Container::value_type,
+            container_mapped_type_traits<Container>::has_mapped_type>::if_not_recursive>::type;
+};
+
+/*
+ * This trait defines the `type_to_check_recursively` which is needed to properly
+ * handle recursively defined traits such as `is_move_constructible` without going
+ * into an infinite recursion.
+ * Should be used instead of directly accessing the `value_type`.
+ * It cancels the recursion by returning the `recursive_bottom` tag.
+ *
+ * The default definition of `type_to_check_recursively` is as follows:
+ *
+ * 1. By default, it is `recursive_bottom`, so that the recursion is canceled.
+ * 2. If the type is non-recursive and defines a `value_type`, then the `value_type` is used.
+ *    If the `value_type` is a pair and a `mapped_type` is defined,
+ *    then the `const` is removed from the first type.
+ * 3. If the type is recursive and `value_type` is not a pair, then `recursive_bottom` is returned.
+ * 4. If the type is recursive and `value_type` is a pair and a `mapped_type` is defined,
+ *    then `const` is removed from the first type and the first type is returned.
+ *
+ * This behavior can be extended by the user as seen in test_stl_binders.cpp.
+ *
+ * This struct is exactly the same as impl_recursive_container_traits.
+ * The duplication achieves that user-defined specializations don't compete
+ * with internal specializations, but take precedence.
+ */
+template <typename Container, typename SFINAE = void>
+struct recursive_container_traits : impl_recursive_container_traits<Container> {};
+
+template <typename T>
+struct is_move_constructible
+    : all_of<std::is_move_constructible<T>,
+             is_move_constructible<
+                 typename recursive_container_traits<T>::type_to_check_recursively>> {};
+
+template <>
+struct is_move_constructible<recursive_bottom> : std::true_type {};
+
+// Likewise for std::pair
+// (after C++17 it is mandatory that the move constructor not exist when the two types aren't
+// themselves move constructible, but this can not be relied upon when T1 or T2 are themselves
+// containers).
+template <typename T1, typename T2>
+struct is_move_constructible<std::pair<T1, T2>>
+    : all_of<is_move_constructible<T1>, is_move_constructible<T2>> {};
+
 // std::is_copy_constructible isn't quite enough: it lets std::vector<T> (and similar) through when
 // T is non-copyable, but code containing such a copy constructor fails to actually compile.
-template <typename T, typename SFINAE = void>
-struct is_copy_constructible : std::is_copy_constructible<T> {};
+template <typename T>
+struct is_copy_constructible
+    : all_of<std::is_copy_constructible<T>,
+             is_copy_constructible<
+                 typename recursive_container_traits<T>::type_to_check_recursively>> {};
 
-// Specialization for types that appear to be copy constructible but also look like stl containers
-// (we specifically check for: has `value_type` and `reference` with `reference = value_type&`): if
-// so, copy constructability depends on whether the value_type is copy constructible.
-template <typename Container>
-struct is_copy_constructible<
-    Container,
-    enable_if_t<
-        all_of<std::is_copy_constructible<Container>,
-               std::is_same<typename Container::value_type &, typename Container::reference>,
-               // Avoid infinite recursion
-               negation<std::is_same<Container, typename Container::value_type>>>::value>>
-    : is_copy_constructible<typename Container::value_type> {};
+template <>
+struct is_copy_constructible<recursive_bottom> : std::true_type {};
 
 // Likewise for std::pair
 // (after C++17 it is mandatory that the copy constructor not exist when the two types aren't
@@ -849,14 +1005,16 @@ struct is_copy_constructible<std::pair<T1, T2>>
     : all_of<is_copy_constructible<T1>, is_copy_constructible<T2>> {};
 
 // The same problems arise with std::is_copy_assignable, so we use the same workaround.
-template <typename T, typename SFINAE = void>
-struct is_copy_assignable : std::is_copy_assignable<T> {};
-template <typename Container>
-struct is_copy_assignable<Container,
-                          enable_if_t<all_of<std::is_copy_assignable<Container>,
-                                             std::is_same<typename Container::value_type &,
-                                                          typename Container::reference>>::value>>
-    : is_copy_assignable<typename Container::value_type> {};
+template <typename T>
+struct is_copy_assignable
+    : all_of<
+          std::is_copy_assignable<T>,
+          is_copy_assignable<typename recursive_container_traits<T>::type_to_check_recursively>> {
+};
+
+template <>
+struct is_copy_assignable<recursive_bottom> : std::true_type {};
+
 template <typename T1, typename T2>
 struct is_copy_assignable<std::pair<T1, T2>>
     : all_of<is_copy_assignable<T1>, is_copy_assignable<T2>> {};
@@ -994,7 +1152,7 @@ protected:
         return [](const void *arg) -> void * { return new T(*reinterpret_cast<const T *>(arg)); };
     }
 
-    template <typename T, typename = enable_if_t<std::is_move_constructible<T>::value>>
+    template <typename T, typename = enable_if_t<is_move_constructible<T>::value>>
     static auto make_move_constructor(const T *)
         -> decltype(new T(std::declval<T &&>()), Constructor{}) {
         return [](const void *arg) -> void * {
@@ -1006,5 +1164,14 @@ protected:
     static Constructor make_move_constructor(...) { return nullptr; }
 };
 
+PYBIND11_NOINLINE std::string type_info_description(const std::type_info &ti) {
+    if (auto *type_data = get_type_info(ti)) {
+        handle th((PyObject *) type_data->type);
+        return th.attr("__module__").cast<std::string>() + '.'
+               + th.attr("__qualname__").cast<std::string>();
+    }
+    return clean_type_id(ti.name());
+}
+
 PYBIND11_NAMESPACE_END(detail)
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
diff --git a/wrap/pybind11/include/pybind11/eigen.h b/wrap/pybind11/include/pybind11/eigen.h
index 4d221b3d7..273b9c930 100644
--- a/wrap/pybind11/include/pybind11/eigen.h
+++ b/wrap/pybind11/include/pybind11/eigen.h
@@ -9,700 +9,4 @@
 
 #pragma once
 
-/* HINT: To suppress warnings originating from the Eigen headers, use -isystem.
-   See also:
-       https://stackoverflow.com/questions/2579576/i-dir-vs-isystem-dir
-       https://stackoverflow.com/questions/1741816/isystem-for-ms-visual-studio-c-compiler
-*/
-
-#include "numpy.h"
-
-// The C4127 suppression was introduced for Eigen 3.4.0. In theory we could
-// make it version specific, or even remove it later, but considering that
-// 1. C4127 is generally far more distracting than useful for modern template code, and
-// 2. we definitely want to ignore any MSVC warnings originating from Eigen code,
-//    it is probably best to keep this around indefinitely.
-#if defined(_MSC_VER)
-#    pragma warning(push)
-#    pragma warning(disable : 4127) // C4127: conditional expression is constant
-#    pragma warning(disable : 5054) // https://github.com/pybind/pybind11/pull/3741
-//       C5054: operator '&': deprecated between enumerations of different types
-#endif
-
-#include <Eigen/Core>
-#include <Eigen/SparseCore>
-
-#if defined(_MSC_VER)
-#    pragma warning(pop)
-#endif
-
-// Eigen prior to 3.2.7 doesn't have proper move constructors--but worse, some classes get implicit
-// move constructors that break things.  We could detect this an explicitly copy, but an extra copy
-// of matrices seems highly undesirable.
-static_assert(EIGEN_VERSION_AT_LEAST(3, 2, 7),
-              "Eigen support in pybind11 requires Eigen >= 3.2.7");
-
-PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
-
-// Provide a convenience alias for easier pass-by-ref usage with fully dynamic strides:
-using EigenDStride = Eigen::Stride<Eigen::Dynamic, Eigen::Dynamic>;
-template <typename MatrixType>
-using EigenDRef = Eigen::Ref<MatrixType, 0, EigenDStride>;
-template <typename MatrixType>
-using EigenDMap = Eigen::Map<MatrixType, 0, EigenDStride>;
-
-PYBIND11_NAMESPACE_BEGIN(detail)
-
-#if EIGEN_VERSION_AT_LEAST(3, 3, 0)
-using EigenIndex = Eigen::Index;
-template <typename Scalar, int Flags, typename StorageIndex>
-using EigenMapSparseMatrix = Eigen::Map<Eigen::SparseMatrix<Scalar, Flags, StorageIndex>>;
-#else
-using EigenIndex = EIGEN_DEFAULT_DENSE_INDEX_TYPE;
-template <typename Scalar, int Flags, typename StorageIndex>
-using EigenMapSparseMatrix = Eigen::MappedSparseMatrix<Scalar, Flags, StorageIndex>;
-#endif
-
-// Matches Eigen::Map, Eigen::Ref, blocks, etc:
-template <typename T>
-using is_eigen_dense_map = all_of<is_template_base_of<Eigen::DenseBase, T>,
-                                  std::is_base_of<Eigen::MapBase<T, Eigen::ReadOnlyAccessors>, T>>;
-template <typename T>
-using is_eigen_mutable_map = std::is_base_of<Eigen::MapBase<T, Eigen::WriteAccessors>, T>;
-template <typename T>
-using is_eigen_dense_plain
-    = all_of<negation<is_eigen_dense_map<T>>, is_template_base_of<Eigen::PlainObjectBase, T>>;
-template <typename T>
-using is_eigen_sparse = is_template_base_of<Eigen::SparseMatrixBase, T>;
-// Test for objects inheriting from EigenBase<Derived> that aren't captured by the above.  This
-// basically covers anything that can be assigned to a dense matrix but that don't have a typical
-// matrix data layout that can be copied from their .data().  For example, DiagonalMatrix and
-// SelfAdjointView fall into this category.
-template <typename T>
-using is_eigen_other
-    = all_of<is_template_base_of<Eigen::EigenBase, T>,
-             negation<any_of<is_eigen_dense_map<T>, is_eigen_dense_plain<T>, is_eigen_sparse<T>>>>;
-
-// Captures numpy/eigen conformability status (returned by EigenProps::conformable()):
-template <bool EigenRowMajor>
-struct EigenConformable {
-    bool conformable = false;
-    EigenIndex rows = 0, cols = 0;
-    EigenDStride stride{0, 0};    // Only valid if negativestrides is false!
-    bool negativestrides = false; // If true, do not use stride!
-
-    // NOLINTNEXTLINE(google-explicit-constructor)
-    EigenConformable(bool fits = false) : conformable{fits} {}
-    // Matrix type:
-    EigenConformable(EigenIndex r, EigenIndex c, EigenIndex rstride, EigenIndex cstride)
-        : conformable{true}, rows{r}, cols{c},
-          // TODO: when Eigen bug #747 is fixed, remove the tests for non-negativity.
-          // http://eigen.tuxfamily.org/bz/show_bug.cgi?id=747
-          stride{EigenRowMajor ? (rstride > 0 ? rstride : 0)
-                               : (cstride > 0 ? cstride : 0) /* outer stride */,
-                 EigenRowMajor ? (cstride > 0 ? cstride : 0)
-                               : (rstride > 0 ? rstride : 0) /* inner stride */},
-          negativestrides{rstride < 0 || cstride < 0} {}
-    // Vector type:
-    EigenConformable(EigenIndex r, EigenIndex c, EigenIndex stride)
-        : EigenConformable(r, c, r == 1 ? c * stride : stride, c == 1 ? r : r * stride) {}
-
-    template <typename props>
-    bool stride_compatible() const {
-        // To have compatible strides, we need (on both dimensions) one of fully dynamic strides,
-        // matching strides, or a dimension size of 1 (in which case the stride value is
-        // irrelevant). Alternatively, if any dimension size is 0, the strides are not relevant
-        // (and numpy ≥ 1.23 sets the strides to 0 in that case, so we need to check explicitly).
-        if (negativestrides) {
-            return false;
-        }
-        if (rows == 0 || cols == 0) {
-            return true;
-        }
-        return (props::inner_stride == Eigen::Dynamic || props::inner_stride == stride.inner()
-                || (EigenRowMajor ? cols : rows) == 1)
-               && (props::outer_stride == Eigen::Dynamic || props::outer_stride == stride.outer()
-                   || (EigenRowMajor ? rows : cols) == 1);
-    }
-    // NOLINTNEXTLINE(google-explicit-constructor)
-    operator bool() const { return conformable; }
-};
-
-template <typename Type>
-struct eigen_extract_stride {
-    using type = Type;
-};
-template <typename PlainObjectType, int MapOptions, typename StrideType>
-struct eigen_extract_stride<Eigen::Map<PlainObjectType, MapOptions, StrideType>> {
-    using type = StrideType;
-};
-template <typename PlainObjectType, int Options, typename StrideType>
-struct eigen_extract_stride<Eigen::Ref<PlainObjectType, Options, StrideType>> {
-    using type = StrideType;
-};
-
-// Helper struct for extracting information from an Eigen type
-template <typename Type_>
-struct EigenProps {
-    using Type = Type_;
-    using Scalar = typename Type::Scalar;
-    using StrideType = typename eigen_extract_stride<Type>::type;
-    static constexpr EigenIndex rows = Type::RowsAtCompileTime, cols = Type::ColsAtCompileTime,
-                                size = Type::SizeAtCompileTime;
-    static constexpr bool row_major = Type::IsRowMajor,
-                          vector
-                          = Type::IsVectorAtCompileTime, // At least one dimension has fixed size 1
-        fixed_rows = rows != Eigen::Dynamic, fixed_cols = cols != Eigen::Dynamic,
-                          fixed = size != Eigen::Dynamic, // Fully-fixed size
-        dynamic = !fixed_rows && !fixed_cols;             // Fully-dynamic size
-
-    template <EigenIndex i, EigenIndex ifzero>
-    using if_zero = std::integral_constant<EigenIndex, i == 0 ? ifzero : i>;
-    static constexpr EigenIndex inner_stride
-        = if_zero<StrideType::InnerStrideAtCompileTime, 1>::value,
-        outer_stride = if_zero < StrideType::OuterStrideAtCompileTime,
-        vector      ? size
-        : row_major ? cols
-                    : rows > ::value;
-    static constexpr bool dynamic_stride
-        = inner_stride == Eigen::Dynamic && outer_stride == Eigen::Dynamic;
-    static constexpr bool requires_row_major
-        = !dynamic_stride && !vector && (row_major ? inner_stride : outer_stride) == 1;
-    static constexpr bool requires_col_major
-        = !dynamic_stride && !vector && (row_major ? outer_stride : inner_stride) == 1;
-
-    // Takes an input array and determines whether we can make it fit into the Eigen type.  If
-    // the array is a vector, we attempt to fit it into either an Eigen 1xN or Nx1 vector
-    // (preferring the latter if it will fit in either, i.e. for a fully dynamic matrix type).
-    static EigenConformable<row_major> conformable(const array &a) {
-        const auto dims = a.ndim();
-        if (dims < 1 || dims > 2) {
-            return false;
-        }
-
-        if (dims == 2) { // Matrix type: require exact match (or dynamic)
-
-            EigenIndex np_rows = a.shape(0), np_cols = a.shape(1),
-                       np_rstride = a.strides(0) / static_cast<ssize_t>(sizeof(Scalar)),
-                       np_cstride = a.strides(1) / static_cast<ssize_t>(sizeof(Scalar));
-            if ((PYBIND11_SILENCE_MSVC_C4127(fixed_rows) && np_rows != rows)
-                || (PYBIND11_SILENCE_MSVC_C4127(fixed_cols) && np_cols != cols)) {
-                return false;
-            }
-
-            return {np_rows, np_cols, np_rstride, np_cstride};
-        }
-
-        // Otherwise we're storing an n-vector.  Only one of the strides will be used, but
-        // whichever is used, we want the (single) numpy stride value.
-        const EigenIndex n = a.shape(0),
-                         stride = a.strides(0) / static_cast<ssize_t>(sizeof(Scalar));
-
-        if (vector) { // Eigen type is a compile-time vector
-            if (PYBIND11_SILENCE_MSVC_C4127(fixed) && size != n) {
-                return false; // Vector size mismatch
-            }
-            return {rows == 1 ? 1 : n, cols == 1 ? 1 : n, stride};
-        }
-        if (fixed) {
-            // The type has a fixed size, but is not a vector: abort
-            return false;
-        }
-        if (fixed_cols) {
-            // Since this isn't a vector, cols must be != 1.  We allow this only if it exactly
-            // equals the number of elements (rows is Dynamic, and so 1 row is allowed).
-            if (cols != n) {
-                return false;
-            }
-            return {1, n, stride};
-        } // Otherwise it's either fully dynamic, or column dynamic; both become a column vector
-        if (PYBIND11_SILENCE_MSVC_C4127(fixed_rows) && rows != n) {
-            return false;
-        }
-        return {n, 1, stride};
-    }
-
-    static constexpr bool show_writeable
-        = is_eigen_dense_map<Type>::value && is_eigen_mutable_map<Type>::value;
-    static constexpr bool show_order = is_eigen_dense_map<Type>::value;
-    static constexpr bool show_c_contiguous = show_order && requires_row_major;
-    static constexpr bool show_f_contiguous
-        = !show_c_contiguous && show_order && requires_col_major;
-
-    static constexpr auto descriptor
-        = const_name("numpy.ndarray[") + npy_format_descriptor<Scalar>::name + const_name("[")
-          + const_name<fixed_rows>(const_name<(size_t) rows>(), const_name("m")) + const_name(", ")
-          + const_name<fixed_cols>(const_name<(size_t) cols>(), const_name("n")) + const_name("]")
-          +
-          // For a reference type (e.g. Ref<MatrixXd>) we have other constraints that might need to
-          // be satisfied: writeable=True (for a mutable reference), and, depending on the map's
-          // stride options, possibly f_contiguous or c_contiguous.  We include them in the
-          // descriptor output to provide some hint as to why a TypeError is occurring (otherwise
-          // it can be confusing to see that a function accepts a 'numpy.ndarray[float64[3,2]]' and
-          // an error message that you *gave* a numpy.ndarray of the right type and dimensions.
-          const_name<show_writeable>(", flags.writeable", "")
-          + const_name<show_c_contiguous>(", flags.c_contiguous", "")
-          + const_name<show_f_contiguous>(", flags.f_contiguous", "") + const_name("]");
-};
-
-// Casts an Eigen type to numpy array.  If given a base, the numpy array references the src data,
-// otherwise it'll make a copy.  writeable lets you turn off the writeable flag for the array.
-template <typename props>
-handle
-eigen_array_cast(typename props::Type const &src, handle base = handle(), bool writeable = true) {
-    constexpr ssize_t elem_size = sizeof(typename props::Scalar);
-    array a;
-    if (props::vector) {
-        a = array({src.size()}, {elem_size * src.innerStride()}, src.data(), base);
-    } else {
-        a = array({src.rows(), src.cols()},
-                  {elem_size * src.rowStride(), elem_size * src.colStride()},
-                  src.data(),
-                  base);
-    }
-
-    if (!writeable) {
-        array_proxy(a.ptr())->flags &= ~detail::npy_api::NPY_ARRAY_WRITEABLE_;
-    }
-
-    return a.release();
-}
-
-// Takes an lvalue ref to some Eigen type and a (python) base object, creating a numpy array that
-// reference the Eigen object's data with `base` as the python-registered base class (if omitted,
-// the base will be set to None, and lifetime management is up to the caller).  The numpy array is
-// non-writeable if the given type is const.
-template <typename props, typename Type>
-handle eigen_ref_array(Type &src, handle parent = none()) {
-    // none here is to get past array's should-we-copy detection, which currently always
-    // copies when there is no base.  Setting the base to None should be harmless.
-    return eigen_array_cast<props>(src, parent, !std::is_const<Type>::value);
-}
-
-// Takes a pointer to some dense, plain Eigen type, builds a capsule around it, then returns a
-// numpy array that references the encapsulated data with a python-side reference to the capsule to
-// tie its destruction to that of any dependent python objects.  Const-ness is determined by
-// whether or not the Type of the pointer given is const.
-template <typename props, typename Type, typename = enable_if_t<is_eigen_dense_plain<Type>::value>>
-handle eigen_encapsulate(Type *src) {
-    capsule base(src, [](void *o) { delete static_cast<Type *>(o); });
-    return eigen_ref_array<props>(*src, base);
-}
-
-// Type caster for regular, dense matrix types (e.g. MatrixXd), but not maps/refs/etc. of dense
-// types.
-template <typename Type>
-struct type_caster<Type, enable_if_t<is_eigen_dense_plain<Type>::value>> {
-    using Scalar = typename Type::Scalar;
-    using props = EigenProps<Type>;
-
-    bool load(handle src, bool convert) {
-        // If we're in no-convert mode, only load if given an array of the correct type
-        if (!convert && !isinstance<array_t<Scalar>>(src)) {
-            return false;
-        }
-
-        // Coerce into an array, but don't do type conversion yet; the copy below handles it.
-        auto buf = array::ensure(src);
-
-        if (!buf) {
-            return false;
-        }
-
-        auto dims = buf.ndim();
-        if (dims < 1 || dims > 2) {
-            return false;
-        }
-
-        auto fits = props::conformable(buf);
-        if (!fits) {
-            return false;
-        }
-
-        // Allocate the new type, then build a numpy reference into it
-        value = Type(fits.rows, fits.cols);
-        auto ref = reinterpret_steal<array>(eigen_ref_array<props>(value));
-        if (dims == 1) {
-            ref = ref.squeeze();
-        } else if (ref.ndim() == 1) {
-            buf = buf.squeeze();
-        }
-
-        int result = detail::npy_api::get().PyArray_CopyInto_(ref.ptr(), buf.ptr());
-
-        if (result < 0) { // Copy failed!
-            PyErr_Clear();
-            return false;
-        }
-
-        return true;
-    }
-
-private:
-    // Cast implementation
-    template <typename CType>
-    static handle cast_impl(CType *src, return_value_policy policy, handle parent) {
-        switch (policy) {
-            case return_value_policy::take_ownership:
-            case return_value_policy::automatic:
-                return eigen_encapsulate<props>(src);
-            case return_value_policy::move:
-                return eigen_encapsulate<props>(new CType(std::move(*src)));
-            case return_value_policy::copy:
-                return eigen_array_cast<props>(*src);
-            case return_value_policy::reference:
-            case return_value_policy::automatic_reference:
-                return eigen_ref_array<props>(*src);
-            case return_value_policy::reference_internal:
-                return eigen_ref_array<props>(*src, parent);
-            default:
-                throw cast_error("unhandled return_value_policy: should not happen!");
-        };
-    }
-
-public:
-    // Normal returned non-reference, non-const value:
-    static handle cast(Type &&src, return_value_policy /* policy */, handle parent) {
-        return cast_impl(&src, return_value_policy::move, parent);
-    }
-    // If you return a non-reference const, we mark the numpy array readonly:
-    static handle cast(const Type &&src, return_value_policy /* policy */, handle parent) {
-        return cast_impl(&src, return_value_policy::move, parent);
-    }
-    // lvalue reference return; default (automatic) becomes copy
-    static handle cast(Type &src, return_value_policy policy, handle parent) {
-        if (policy == return_value_policy::automatic
-            || policy == return_value_policy::automatic_reference) {
-            policy = return_value_policy::copy;
-        }
-        return cast_impl(&src, policy, parent);
-    }
-    // const lvalue reference return; default (automatic) becomes copy
-    static handle cast(const Type &src, return_value_policy policy, handle parent) {
-        if (policy == return_value_policy::automatic
-            || policy == return_value_policy::automatic_reference) {
-            policy = return_value_policy::copy;
-        }
-        return cast(&src, policy, parent);
-    }
-    // non-const pointer return
-    static handle cast(Type *src, return_value_policy policy, handle parent) {
-        return cast_impl(src, policy, parent);
-    }
-    // const pointer return
-    static handle cast(const Type *src, return_value_policy policy, handle parent) {
-        return cast_impl(src, policy, parent);
-    }
-
-    static constexpr auto name = props::descriptor;
-
-    // NOLINTNEXTLINE(google-explicit-constructor)
-    operator Type *() { return &value; }
-    // NOLINTNEXTLINE(google-explicit-constructor)
-    operator Type &() { return value; }
-    // NOLINTNEXTLINE(google-explicit-constructor)
-    operator Type &&() && { return std::move(value); }
-    template <typename T>
-    using cast_op_type = movable_cast_op_type<T>;
-
-private:
-    Type value;
-};
-
-// Base class for casting reference/map/block/etc. objects back to python.
-template <typename MapType>
-struct eigen_map_caster {
-private:
-    using props = EigenProps<MapType>;
-
-public:
-    // Directly referencing a ref/map's data is a bit dangerous (whatever the map/ref points to has
-    // to stay around), but we'll allow it under the assumption that you know what you're doing
-    // (and have an appropriate keep_alive in place).  We return a numpy array pointing directly at
-    // the ref's data (The numpy array ends up read-only if the ref was to a const matrix type.)
-    // Note that this means you need to ensure you don't destroy the object in some other way (e.g.
-    // with an appropriate keep_alive, or with a reference to a statically allocated matrix).
-    static handle cast(const MapType &src, return_value_policy policy, handle parent) {
-        switch (policy) {
-            case return_value_policy::copy:
-                return eigen_array_cast<props>(src);
-            case return_value_policy::reference_internal:
-                return eigen_array_cast<props>(src, parent, is_eigen_mutable_map<MapType>::value);
-            case return_value_policy::reference:
-            case return_value_policy::automatic:
-            case return_value_policy::automatic_reference:
-                return eigen_array_cast<props>(src, none(), is_eigen_mutable_map<MapType>::value);
-            default:
-                // move, take_ownership don't make any sense for a ref/map:
-                pybind11_fail("Invalid return_value_policy for Eigen Map/Ref/Block type");
-        }
-    }
-
-    static constexpr auto name = props::descriptor;
-
-    // Explicitly delete these: support python -> C++ conversion on these (i.e. these can be return
-    // types but not bound arguments).  We still provide them (with an explicitly delete) so that
-    // you end up here if you try anyway.
-    bool load(handle, bool) = delete;
-    operator MapType() = delete;
-    template <typename>
-    using cast_op_type = MapType;
-};
-
-// We can return any map-like object (but can only load Refs, specialized next):
-template <typename Type>
-struct type_caster<Type, enable_if_t<is_eigen_dense_map<Type>::value>> : eigen_map_caster<Type> {};
-
-// Loader for Ref<...> arguments.  See the documentation for info on how to make this work without
-// copying (it requires some extra effort in many cases).
-template <typename PlainObjectType, typename StrideType>
-struct type_caster<
-    Eigen::Ref<PlainObjectType, 0, StrideType>,
-    enable_if_t<is_eigen_dense_map<Eigen::Ref<PlainObjectType, 0, StrideType>>::value>>
-    : public eigen_map_caster<Eigen::Ref<PlainObjectType, 0, StrideType>> {
-private:
-    using Type = Eigen::Ref<PlainObjectType, 0, StrideType>;
-    using props = EigenProps<Type>;
-    using Scalar = typename props::Scalar;
-    using MapType = Eigen::Map<PlainObjectType, 0, StrideType>;
-    using Array
-        = array_t<Scalar,
-                  array::forcecast
-                      | ((props::row_major ? props::inner_stride : props::outer_stride) == 1
-                             ? array::c_style
-                         : (props::row_major ? props::outer_stride : props::inner_stride) == 1
-                             ? array::f_style
-                             : 0)>;
-    static constexpr bool need_writeable = is_eigen_mutable_map<Type>::value;
-    // Delay construction (these have no default constructor)
-    std::unique_ptr<MapType> map;
-    std::unique_ptr<Type> ref;
-    // Our array.  When possible, this is just a numpy array pointing to the source data, but
-    // sometimes we can't avoid copying (e.g. input is not a numpy array at all, has an
-    // incompatible layout, or is an array of a type that needs to be converted).  Using a numpy
-    // temporary (rather than an Eigen temporary) saves an extra copy when we need both type
-    // conversion and storage order conversion.  (Note that we refuse to use this temporary copy
-    // when loading an argument for a Ref<M> with M non-const, i.e. a read-write reference).
-    Array copy_or_ref;
-
-public:
-    bool load(handle src, bool convert) {
-        // First check whether what we have is already an array of the right type.  If not, we
-        // can't avoid a copy (because the copy is also going to do type conversion).
-        bool need_copy = !isinstance<Array>(src);
-
-        EigenConformable<props::row_major> fits;
-        if (!need_copy) {
-            // We don't need a converting copy, but we also need to check whether the strides are
-            // compatible with the Ref's stride requirements
-            auto aref = reinterpret_borrow<Array>(src);
-
-            if (aref && (!need_writeable || aref.writeable())) {
-                fits = props::conformable(aref);
-                if (!fits) {
-                    return false; // Incompatible dimensions
-                }
-                if (!fits.template stride_compatible<props>()) {
-                    need_copy = true;
-                } else {
-                    copy_or_ref = std::move(aref);
-                }
-            } else {
-                need_copy = true;
-            }
-        }
-
-        if (need_copy) {
-            // We need to copy: If we need a mutable reference, or we're not supposed to convert
-            // (either because we're in the no-convert overload pass, or because we're explicitly
-            // instructed not to copy (via `py::arg().noconvert()`) we have to fail loading.
-            if (!convert || need_writeable) {
-                return false;
-            }
-
-            Array copy = Array::ensure(src);
-            if (!copy) {
-                return false;
-            }
-            fits = props::conformable(copy);
-            if (!fits || !fits.template stride_compatible<props>()) {
-                return false;
-            }
-            copy_or_ref = std::move(copy);
-            loader_life_support::add_patient(copy_or_ref);
-        }
-
-        ref.reset();
-        map.reset(new MapType(data(copy_or_ref),
-                              fits.rows,
-                              fits.cols,
-                              make_stride(fits.stride.outer(), fits.stride.inner())));
-        ref.reset(new Type(*map));
-
-        return true;
-    }
-
-    // NOLINTNEXTLINE(google-explicit-constructor)
-    operator Type *() { return ref.get(); }
-    // NOLINTNEXTLINE(google-explicit-constructor)
-    operator Type &() { return *ref; }
-    template <typename _T>
-    using cast_op_type = pybind11::detail::cast_op_type<_T>;
-
-private:
-    template <typename T = Type, enable_if_t<is_eigen_mutable_map<T>::value, int> = 0>
-    Scalar *data(Array &a) {
-        return a.mutable_data();
-    }
-
-    template <typename T = Type, enable_if_t<!is_eigen_mutable_map<T>::value, int> = 0>
-    const Scalar *data(Array &a) {
-        return a.data();
-    }
-
-    // Attempt to figure out a constructor of `Stride` that will work.
-    // If both strides are fixed, use a default constructor:
-    template <typename S>
-    using stride_ctor_default = bool_constant<S::InnerStrideAtCompileTime != Eigen::Dynamic
-                                              && S::OuterStrideAtCompileTime != Eigen::Dynamic
-                                              && std::is_default_constructible<S>::value>;
-    // Otherwise, if there is a two-index constructor, assume it is (outer,inner) like
-    // Eigen::Stride, and use it:
-    template <typename S>
-    using stride_ctor_dual
-        = bool_constant<!stride_ctor_default<S>::value
-                        && std::is_constructible<S, EigenIndex, EigenIndex>::value>;
-    // Otherwise, if there is a one-index constructor, and just one of the strides is dynamic, use
-    // it (passing whichever stride is dynamic).
-    template <typename S>
-    using stride_ctor_outer
-        = bool_constant<!any_of<stride_ctor_default<S>, stride_ctor_dual<S>>::value
-                        && S::OuterStrideAtCompileTime == Eigen::Dynamic
-                        && S::InnerStrideAtCompileTime != Eigen::Dynamic
-                        && std::is_constructible<S, EigenIndex>::value>;
-    template <typename S>
-    using stride_ctor_inner
-        = bool_constant<!any_of<stride_ctor_default<S>, stride_ctor_dual<S>>::value
-                        && S::InnerStrideAtCompileTime == Eigen::Dynamic
-                        && S::OuterStrideAtCompileTime != Eigen::Dynamic
-                        && std::is_constructible<S, EigenIndex>::value>;
-
-    template <typename S = StrideType, enable_if_t<stride_ctor_default<S>::value, int> = 0>
-    static S make_stride(EigenIndex, EigenIndex) {
-        return S();
-    }
-    template <typename S = StrideType, enable_if_t<stride_ctor_dual<S>::value, int> = 0>
-    static S make_stride(EigenIndex outer, EigenIndex inner) {
-        return S(outer, inner);
-    }
-    template <typename S = StrideType, enable_if_t<stride_ctor_outer<S>::value, int> = 0>
-    static S make_stride(EigenIndex outer, EigenIndex) {
-        return S(outer);
-    }
-    template <typename S = StrideType, enable_if_t<stride_ctor_inner<S>::value, int> = 0>
-    static S make_stride(EigenIndex, EigenIndex inner) {
-        return S(inner);
-    }
-};
-
-// type_caster for special matrix types (e.g. DiagonalMatrix), which are EigenBase, but not
-// EigenDense (i.e. they don't have a data(), at least not with the usual matrix layout).
-// load() is not supported, but we can cast them into the python domain by first copying to a
-// regular Eigen::Matrix, then casting that.
-template <typename Type>
-struct type_caster<Type, enable_if_t<is_eigen_other<Type>::value>> {
-protected:
-    using Matrix
-        = Eigen::Matrix<typename Type::Scalar, Type::RowsAtCompileTime, Type::ColsAtCompileTime>;
-    using props = EigenProps<Matrix>;
-
-public:
-    static handle cast(const Type &src, return_value_policy /* policy */, handle /* parent */) {
-        handle h = eigen_encapsulate<props>(new Matrix(src));
-        return h;
-    }
-    static handle cast(const Type *src, return_value_policy policy, handle parent) {
-        return cast(*src, policy, parent);
-    }
-
-    static constexpr auto name = props::descriptor;
-
-    // Explicitly delete these: support python -> C++ conversion on these (i.e. these can be return
-    // types but not bound arguments).  We still provide them (with an explicitly delete) so that
-    // you end up here if you try anyway.
-    bool load(handle, bool) = delete;
-    operator Type() = delete;
-    template <typename>
-    using cast_op_type = Type;
-};
-
-template <typename Type>
-struct type_caster<Type, enable_if_t<is_eigen_sparse<Type>::value>> {
-    using Scalar = typename Type::Scalar;
-    using StorageIndex = remove_reference_t<decltype(*std::declval<Type>().outerIndexPtr())>;
-    using Index = typename Type::Index;
-    static constexpr bool rowMajor = Type::IsRowMajor;
-
-    bool load(handle src, bool) {
-        if (!src) {
-            return false;
-        }
-
-        auto obj = reinterpret_borrow<object>(src);
-        object sparse_module = module_::import("scipy.sparse");
-        object matrix_type = sparse_module.attr(rowMajor ? "csr_matrix" : "csc_matrix");
-
-        if (!type::handle_of(obj).is(matrix_type)) {
-            try {
-                obj = matrix_type(obj);
-            } catch (const error_already_set &) {
-                return false;
-            }
-        }
-
-        auto values = array_t<Scalar>((object) obj.attr("data"));
-        auto innerIndices = array_t<StorageIndex>((object) obj.attr("indices"));
-        auto outerIndices = array_t<StorageIndex>((object) obj.attr("indptr"));
-        auto shape = pybind11::tuple((pybind11::object) obj.attr("shape"));
-        auto nnz = obj.attr("nnz").cast<Index>();
-
-        if (!values || !innerIndices || !outerIndices) {
-            return false;
-        }
-
-        value = EigenMapSparseMatrix<Scalar,
-                                     Type::Flags &(Eigen::RowMajor | Eigen::ColMajor),
-                                     StorageIndex>(shape[0].cast<Index>(),
-                                                   shape[1].cast<Index>(),
-                                                   std::move(nnz),
-                                                   outerIndices.mutable_data(),
-                                                   innerIndices.mutable_data(),
-                                                   values.mutable_data());
-
-        return true;
-    }
-
-    static handle cast(const Type &src, return_value_policy /* policy */, handle /* parent */) {
-        const_cast<Type &>(src).makeCompressed();
-
-        object matrix_type
-            = module_::import("scipy.sparse").attr(rowMajor ? "csr_matrix" : "csc_matrix");
-
-        array data(src.nonZeros(), src.valuePtr());
-        array outerIndices((rowMajor ? src.rows() : src.cols()) + 1, src.outerIndexPtr());
-        array innerIndices(src.nonZeros(), src.innerIndexPtr());
-
-        return matrix_type(pybind11::make_tuple(
-                               std::move(data), std::move(innerIndices), std::move(outerIndices)),
-                           pybind11::make_tuple(src.rows(), src.cols()))
-            .release();
-    }
-
-    PYBIND11_TYPE_CASTER(Type,
-                         const_name<(Type::IsRowMajor) != 0>("scipy.sparse.csr_matrix[",
-                                                             "scipy.sparse.csc_matrix[")
-                             + npy_format_descriptor<Scalar>::name + const_name("]"));
-};
-
-PYBIND11_NAMESPACE_END(detail)
-PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
+#include "eigen/matrix.h"
diff --git a/wrap/pybind11/include/pybind11/eigen/common.h b/wrap/pybind11/include/pybind11/eigen/common.h
new file mode 100644
index 000000000..24f56d158
--- /dev/null
+++ b/wrap/pybind11/include/pybind11/eigen/common.h
@@ -0,0 +1,9 @@
+// Copyright (c) 2023 The pybind Community.
+
+#pragma once
+
+// Common message for `static_assert()`s, which are useful to easily
+// preempt much less obvious errors.
+#define PYBIND11_EIGEN_MESSAGE_POINTER_TYPES_ARE_NOT_SUPPORTED                                    \
+    "Pointer types (in particular `PyObject *`) are not supported as scalar types for Eigen "     \
+    "types."
diff --git a/wrap/pybind11/include/pybind11/eigen/matrix.h b/wrap/pybind11/include/pybind11/eigen/matrix.h
new file mode 100644
index 000000000..8d4342f81
--- /dev/null
+++ b/wrap/pybind11/include/pybind11/eigen/matrix.h
@@ -0,0 +1,714 @@
+/*
+    pybind11/eigen/matrix.h: Transparent conversion for dense and sparse Eigen matrices
+
+    Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#pragma once
+
+#include "../numpy.h"
+#include "common.h"
+
+/* HINT: To suppress warnings originating from the Eigen headers, use -isystem.
+   See also:
+       https://stackoverflow.com/questions/2579576/i-dir-vs-isystem-dir
+       https://stackoverflow.com/questions/1741816/isystem-for-ms-visual-studio-c-compiler
+*/
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_MSVC(5054) // https://github.com/pybind/pybind11/pull/3741
+//       C5054: operator '&': deprecated between enumerations of different types
+#if defined(__MINGW32__)
+PYBIND11_WARNING_DISABLE_GCC("-Wmaybe-uninitialized")
+#endif
+
+#include <Eigen/Core>
+#include <Eigen/SparseCore>
+
+PYBIND11_WARNING_POP
+
+// Eigen prior to 3.2.7 doesn't have proper move constructors--but worse, some classes get implicit
+// move constructors that break things.  We could detect this an explicitly copy, but an extra copy
+// of matrices seems highly undesirable.
+static_assert(EIGEN_VERSION_AT_LEAST(3, 2, 7),
+              "Eigen matrix support in pybind11 requires Eigen >= 3.2.7");
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
+// Provide a convenience alias for easier pass-by-ref usage with fully dynamic strides:
+using EigenDStride = Eigen::Stride<Eigen::Dynamic, Eigen::Dynamic>;
+template <typename MatrixType>
+using EigenDRef = Eigen::Ref<MatrixType, 0, EigenDStride>;
+template <typename MatrixType>
+using EigenDMap = Eigen::Map<MatrixType, 0, EigenDStride>;
+
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+#if EIGEN_VERSION_AT_LEAST(3, 3, 0)
+using EigenIndex = Eigen::Index;
+template <typename Scalar, int Flags, typename StorageIndex>
+using EigenMapSparseMatrix = Eigen::Map<Eigen::SparseMatrix<Scalar, Flags, StorageIndex>>;
+#else
+using EigenIndex = EIGEN_DEFAULT_DENSE_INDEX_TYPE;
+template <typename Scalar, int Flags, typename StorageIndex>
+using EigenMapSparseMatrix = Eigen::MappedSparseMatrix<Scalar, Flags, StorageIndex>;
+#endif
+
+// Matches Eigen::Map, Eigen::Ref, blocks, etc:
+template <typename T>
+using is_eigen_dense_map = all_of<is_template_base_of<Eigen::DenseBase, T>,
+                                  std::is_base_of<Eigen::MapBase<T, Eigen::ReadOnlyAccessors>, T>>;
+template <typename T>
+using is_eigen_mutable_map = std::is_base_of<Eigen::MapBase<T, Eigen::WriteAccessors>, T>;
+template <typename T>
+using is_eigen_dense_plain
+    = all_of<negation<is_eigen_dense_map<T>>, is_template_base_of<Eigen::PlainObjectBase, T>>;
+template <typename T>
+using is_eigen_sparse = is_template_base_of<Eigen::SparseMatrixBase, T>;
+// Test for objects inheriting from EigenBase<Derived> that aren't captured by the above.  This
+// basically covers anything that can be assigned to a dense matrix but that don't have a typical
+// matrix data layout that can be copied from their .data().  For example, DiagonalMatrix and
+// SelfAdjointView fall into this category.
+template <typename T>
+using is_eigen_other
+    = all_of<is_template_base_of<Eigen::EigenBase, T>,
+             negation<any_of<is_eigen_dense_map<T>, is_eigen_dense_plain<T>, is_eigen_sparse<T>>>>;
+
+// Captures numpy/eigen conformability status (returned by EigenProps::conformable()):
+template <bool EigenRowMajor>
+struct EigenConformable {
+    bool conformable = false;
+    EigenIndex rows = 0, cols = 0;
+    EigenDStride stride{0, 0};    // Only valid if negativestrides is false!
+    bool negativestrides = false; // If true, do not use stride!
+
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    EigenConformable(bool fits = false) : conformable{fits} {}
+    // Matrix type:
+    EigenConformable(EigenIndex r, EigenIndex c, EigenIndex rstride, EigenIndex cstride)
+        : conformable{true}, rows{r}, cols{c},
+          // TODO: when Eigen bug #747 is fixed, remove the tests for non-negativity.
+          // http://eigen.tuxfamily.org/bz/show_bug.cgi?id=747
+          stride{EigenRowMajor ? (rstride > 0 ? rstride : 0)
+                               : (cstride > 0 ? cstride : 0) /* outer stride */,
+                 EigenRowMajor ? (cstride > 0 ? cstride : 0)
+                               : (rstride > 0 ? rstride : 0) /* inner stride */},
+          negativestrides{rstride < 0 || cstride < 0} {}
+    // Vector type:
+    EigenConformable(EigenIndex r, EigenIndex c, EigenIndex stride)
+        : EigenConformable(r, c, r == 1 ? c * stride : stride, c == 1 ? r : r * stride) {}
+
+    template <typename props>
+    bool stride_compatible() const {
+        // To have compatible strides, we need (on both dimensions) one of fully dynamic strides,
+        // matching strides, or a dimension size of 1 (in which case the stride value is
+        // irrelevant). Alternatively, if any dimension size is 0, the strides are not relevant
+        // (and numpy ≥ 1.23 sets the strides to 0 in that case, so we need to check explicitly).
+        if (negativestrides) {
+            return false;
+        }
+        if (rows == 0 || cols == 0) {
+            return true;
+        }
+        return (props::inner_stride == Eigen::Dynamic || props::inner_stride == stride.inner()
+                || (EigenRowMajor ? cols : rows) == 1)
+               && (props::outer_stride == Eigen::Dynamic || props::outer_stride == stride.outer()
+                   || (EigenRowMajor ? rows : cols) == 1);
+    }
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator bool() const { return conformable; }
+};
+
+template <typename Type>
+struct eigen_extract_stride {
+    using type = Type;
+};
+template <typename PlainObjectType, int MapOptions, typename StrideType>
+struct eigen_extract_stride<Eigen::Map<PlainObjectType, MapOptions, StrideType>> {
+    using type = StrideType;
+};
+template <typename PlainObjectType, int Options, typename StrideType>
+struct eigen_extract_stride<Eigen::Ref<PlainObjectType, Options, StrideType>> {
+    using type = StrideType;
+};
+
+// Helper struct for extracting information from an Eigen type
+template <typename Type_>
+struct EigenProps {
+    using Type = Type_;
+    using Scalar = typename Type::Scalar;
+    using StrideType = typename eigen_extract_stride<Type>::type;
+    static constexpr EigenIndex rows = Type::RowsAtCompileTime, cols = Type::ColsAtCompileTime,
+                                size = Type::SizeAtCompileTime;
+    static constexpr bool row_major = Type::IsRowMajor,
+                          vector
+                          = Type::IsVectorAtCompileTime, // At least one dimension has fixed size 1
+        fixed_rows = rows != Eigen::Dynamic, fixed_cols = cols != Eigen::Dynamic,
+                          fixed = size != Eigen::Dynamic, // Fully-fixed size
+        dynamic = !fixed_rows && !fixed_cols;             // Fully-dynamic size
+
+    template <EigenIndex i, EigenIndex ifzero>
+    using if_zero = std::integral_constant<EigenIndex, i == 0 ? ifzero : i>;
+    static constexpr EigenIndex inner_stride
+        = if_zero<StrideType::InnerStrideAtCompileTime, 1>::value,
+        outer_stride = if_zero < StrideType::OuterStrideAtCompileTime,
+        vector      ? size
+        : row_major ? cols
+                    : rows > ::value;
+    static constexpr bool dynamic_stride
+        = inner_stride == Eigen::Dynamic && outer_stride == Eigen::Dynamic;
+    static constexpr bool requires_row_major
+        = !dynamic_stride && !vector && (row_major ? inner_stride : outer_stride) == 1;
+    static constexpr bool requires_col_major
+        = !dynamic_stride && !vector && (row_major ? outer_stride : inner_stride) == 1;
+
+    // Takes an input array and determines whether we can make it fit into the Eigen type.  If
+    // the array is a vector, we attempt to fit it into either an Eigen 1xN or Nx1 vector
+    // (preferring the latter if it will fit in either, i.e. for a fully dynamic matrix type).
+    static EigenConformable<row_major> conformable(const array &a) {
+        const auto dims = a.ndim();
+        if (dims < 1 || dims > 2) {
+            return false;
+        }
+
+        if (dims == 2) { // Matrix type: require exact match (or dynamic)
+
+            EigenIndex np_rows = a.shape(0), np_cols = a.shape(1),
+                       np_rstride = a.strides(0) / static_cast<ssize_t>(sizeof(Scalar)),
+                       np_cstride = a.strides(1) / static_cast<ssize_t>(sizeof(Scalar));
+            if ((fixed_rows && np_rows != rows) || (fixed_cols && np_cols != cols)) {
+                return false;
+            }
+
+            return {np_rows, np_cols, np_rstride, np_cstride};
+        }
+
+        // Otherwise we're storing an n-vector.  Only one of the strides will be used, but
+        // whichever is used, we want the (single) numpy stride value.
+        const EigenIndex n = a.shape(0),
+                         stride = a.strides(0) / static_cast<ssize_t>(sizeof(Scalar));
+
+        if (vector) { // Eigen type is a compile-time vector
+            if (fixed && size != n) {
+                return false; // Vector size mismatch
+            }
+            return {rows == 1 ? 1 : n, cols == 1 ? 1 : n, stride};
+        }
+        if (fixed) {
+            // The type has a fixed size, but is not a vector: abort
+            return false;
+        }
+        if (fixed_cols) {
+            // Since this isn't a vector, cols must be != 1.  We allow this only if it exactly
+            // equals the number of elements (rows is Dynamic, and so 1 row is allowed).
+            if (cols != n) {
+                return false;
+            }
+            return {1, n, stride};
+        } // Otherwise it's either fully dynamic, or column dynamic; both become a column vector
+        if (fixed_rows && rows != n) {
+            return false;
+        }
+        return {n, 1, stride};
+    }
+
+    static constexpr bool show_writeable
+        = is_eigen_dense_map<Type>::value && is_eigen_mutable_map<Type>::value;
+    static constexpr bool show_order = is_eigen_dense_map<Type>::value;
+    static constexpr bool show_c_contiguous = show_order && requires_row_major;
+    static constexpr bool show_f_contiguous
+        = !show_c_contiguous && show_order && requires_col_major;
+
+    static constexpr auto descriptor
+        = const_name("numpy.ndarray[") + npy_format_descriptor<Scalar>::name + const_name("[")
+          + const_name<fixed_rows>(const_name<(size_t) rows>(), const_name("m")) + const_name(", ")
+          + const_name<fixed_cols>(const_name<(size_t) cols>(), const_name("n")) + const_name("]")
+          +
+          // For a reference type (e.g. Ref<MatrixXd>) we have other constraints that might need to
+          // be satisfied: writeable=True (for a mutable reference), and, depending on the map's
+          // stride options, possibly f_contiguous or c_contiguous.  We include them in the
+          // descriptor output to provide some hint as to why a TypeError is occurring (otherwise
+          // it can be confusing to see that a function accepts a 'numpy.ndarray[float64[3,2]]' and
+          // an error message that you *gave* a numpy.ndarray of the right type and dimensions.
+          const_name<show_writeable>(", flags.writeable", "")
+          + const_name<show_c_contiguous>(", flags.c_contiguous", "")
+          + const_name<show_f_contiguous>(", flags.f_contiguous", "") + const_name("]");
+};
+
+// Casts an Eigen type to numpy array.  If given a base, the numpy array references the src data,
+// otherwise it'll make a copy.  writeable lets you turn off the writeable flag for the array.
+template <typename props>
+handle
+eigen_array_cast(typename props::Type const &src, handle base = handle(), bool writeable = true) {
+    constexpr ssize_t elem_size = sizeof(typename props::Scalar);
+    array a;
+    if (props::vector) {
+        a = array({src.size()}, {elem_size * src.innerStride()}, src.data(), base);
+    } else {
+        a = array({src.rows(), src.cols()},
+                  {elem_size * src.rowStride(), elem_size * src.colStride()},
+                  src.data(),
+                  base);
+    }
+
+    if (!writeable) {
+        array_proxy(a.ptr())->flags &= ~detail::npy_api::NPY_ARRAY_WRITEABLE_;
+    }
+
+    return a.release();
+}
+
+// Takes an lvalue ref to some Eigen type and a (python) base object, creating a numpy array that
+// reference the Eigen object's data with `base` as the python-registered base class (if omitted,
+// the base will be set to None, and lifetime management is up to the caller).  The numpy array is
+// non-writeable if the given type is const.
+template <typename props, typename Type>
+handle eigen_ref_array(Type &src, handle parent = none()) {
+    // none here is to get past array's should-we-copy detection, which currently always
+    // copies when there is no base.  Setting the base to None should be harmless.
+    return eigen_array_cast<props>(src, parent, !std::is_const<Type>::value);
+}
+
+// Takes a pointer to some dense, plain Eigen type, builds a capsule around it, then returns a
+// numpy array that references the encapsulated data with a python-side reference to the capsule to
+// tie its destruction to that of any dependent python objects.  Const-ness is determined by
+// whether or not the Type of the pointer given is const.
+template <typename props, typename Type, typename = enable_if_t<is_eigen_dense_plain<Type>::value>>
+handle eigen_encapsulate(Type *src) {
+    capsule base(src, [](void *o) { delete static_cast<Type *>(o); });
+    return eigen_ref_array<props>(*src, base);
+}
+
+// Type caster for regular, dense matrix types (e.g. MatrixXd), but not maps/refs/etc. of dense
+// types.
+template <typename Type>
+struct type_caster<Type, enable_if_t<is_eigen_dense_plain<Type>::value>> {
+    using Scalar = typename Type::Scalar;
+    static_assert(!std::is_pointer<Scalar>::value,
+                  PYBIND11_EIGEN_MESSAGE_POINTER_TYPES_ARE_NOT_SUPPORTED);
+    using props = EigenProps<Type>;
+
+    bool load(handle src, bool convert) {
+        // If we're in no-convert mode, only load if given an array of the correct type
+        if (!convert && !isinstance<array_t<Scalar>>(src)) {
+            return false;
+        }
+
+        // Coerce into an array, but don't do type conversion yet; the copy below handles it.
+        auto buf = array::ensure(src);
+
+        if (!buf) {
+            return false;
+        }
+
+        auto dims = buf.ndim();
+        if (dims < 1 || dims > 2) {
+            return false;
+        }
+
+        auto fits = props::conformable(buf);
+        if (!fits) {
+            return false;
+        }
+
+        // Allocate the new type, then build a numpy reference into it
+        value = Type(fits.rows, fits.cols);
+        auto ref = reinterpret_steal<array>(eigen_ref_array<props>(value));
+        if (dims == 1) {
+            ref = ref.squeeze();
+        } else if (ref.ndim() == 1) {
+            buf = buf.squeeze();
+        }
+
+        int result = detail::npy_api::get().PyArray_CopyInto_(ref.ptr(), buf.ptr());
+
+        if (result < 0) { // Copy failed!
+            PyErr_Clear();
+            return false;
+        }
+
+        return true;
+    }
+
+private:
+    // Cast implementation
+    template <typename CType>
+    static handle cast_impl(CType *src, return_value_policy policy, handle parent) {
+        switch (policy) {
+            case return_value_policy::take_ownership:
+            case return_value_policy::automatic:
+                return eigen_encapsulate<props>(src);
+            case return_value_policy::move:
+                return eigen_encapsulate<props>(new CType(std::move(*src)));
+            case return_value_policy::copy:
+                return eigen_array_cast<props>(*src);
+            case return_value_policy::reference:
+            case return_value_policy::automatic_reference:
+                return eigen_ref_array<props>(*src);
+            case return_value_policy::reference_internal:
+                return eigen_ref_array<props>(*src, parent);
+            default:
+                throw cast_error("unhandled return_value_policy: should not happen!");
+        };
+    }
+
+public:
+    // Normal returned non-reference, non-const value:
+    static handle cast(Type &&src, return_value_policy /* policy */, handle parent) {
+        return cast_impl(&src, return_value_policy::move, parent);
+    }
+    // If you return a non-reference const, we mark the numpy array readonly:
+    static handle cast(const Type &&src, return_value_policy /* policy */, handle parent) {
+        return cast_impl(&src, return_value_policy::move, parent);
+    }
+    // lvalue reference return; default (automatic) becomes copy
+    static handle cast(Type &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic
+            || policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::copy;
+        }
+        return cast_impl(&src, policy, parent);
+    }
+    // const lvalue reference return; default (automatic) becomes copy
+    static handle cast(const Type &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic
+            || policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::copy;
+        }
+        return cast(&src, policy, parent);
+    }
+    // non-const pointer return
+    static handle cast(Type *src, return_value_policy policy, handle parent) {
+        return cast_impl(src, policy, parent);
+    }
+    // const pointer return
+    static handle cast(const Type *src, return_value_policy policy, handle parent) {
+        return cast_impl(src, policy, parent);
+    }
+
+    static constexpr auto name = props::descriptor;
+
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator Type *() { return &value; }
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator Type &() { return value; }
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator Type &&() && { return std::move(value); }
+    template <typename T>
+    using cast_op_type = movable_cast_op_type<T>;
+
+private:
+    Type value;
+};
+
+// Base class for casting reference/map/block/etc. objects back to python.
+template <typename MapType>
+struct eigen_map_caster {
+    static_assert(!std::is_pointer<typename MapType::Scalar>::value,
+                  PYBIND11_EIGEN_MESSAGE_POINTER_TYPES_ARE_NOT_SUPPORTED);
+
+private:
+    using props = EigenProps<MapType>;
+
+public:
+    // Directly referencing a ref/map's data is a bit dangerous (whatever the map/ref points to has
+    // to stay around), but we'll allow it under the assumption that you know what you're doing
+    // (and have an appropriate keep_alive in place).  We return a numpy array pointing directly at
+    // the ref's data (The numpy array ends up read-only if the ref was to a const matrix type.)
+    // Note that this means you need to ensure you don't destroy the object in some other way (e.g.
+    // with an appropriate keep_alive, or with a reference to a statically allocated matrix).
+    static handle cast(const MapType &src, return_value_policy policy, handle parent) {
+        switch (policy) {
+            case return_value_policy::copy:
+                return eigen_array_cast<props>(src);
+            case return_value_policy::reference_internal:
+                return eigen_array_cast<props>(src, parent, is_eigen_mutable_map<MapType>::value);
+            case return_value_policy::reference:
+            case return_value_policy::automatic:
+            case return_value_policy::automatic_reference:
+                return eigen_array_cast<props>(src, none(), is_eigen_mutable_map<MapType>::value);
+            default:
+                // move, take_ownership don't make any sense for a ref/map:
+                pybind11_fail("Invalid return_value_policy for Eigen Map/Ref/Block type");
+        }
+    }
+
+    static constexpr auto name = props::descriptor;
+
+    // Explicitly delete these: support python -> C++ conversion on these (i.e. these can be return
+    // types but not bound arguments).  We still provide them (with an explicitly delete) so that
+    // you end up here if you try anyway.
+    bool load(handle, bool) = delete;
+    operator MapType() = delete;
+    template <typename>
+    using cast_op_type = MapType;
+};
+
+// We can return any map-like object (but can only load Refs, specialized next):
+template <typename Type>
+struct type_caster<Type, enable_if_t<is_eigen_dense_map<Type>::value>> : eigen_map_caster<Type> {};
+
+// Loader for Ref<...> arguments.  See the documentation for info on how to make this work without
+// copying (it requires some extra effort in many cases).
+template <typename PlainObjectType, typename StrideType>
+struct type_caster<
+    Eigen::Ref<PlainObjectType, 0, StrideType>,
+    enable_if_t<is_eigen_dense_map<Eigen::Ref<PlainObjectType, 0, StrideType>>::value>>
+    : public eigen_map_caster<Eigen::Ref<PlainObjectType, 0, StrideType>> {
+private:
+    using Type = Eigen::Ref<PlainObjectType, 0, StrideType>;
+    using props = EigenProps<Type>;
+    using Scalar = typename props::Scalar;
+    static_assert(!std::is_pointer<Scalar>::value,
+                  PYBIND11_EIGEN_MESSAGE_POINTER_TYPES_ARE_NOT_SUPPORTED);
+    using MapType = Eigen::Map<PlainObjectType, 0, StrideType>;
+    using Array
+        = array_t<Scalar,
+                  array::forcecast
+                      | ((props::row_major ? props::inner_stride : props::outer_stride) == 1
+                             ? array::c_style
+                         : (props::row_major ? props::outer_stride : props::inner_stride) == 1
+                             ? array::f_style
+                             : 0)>;
+    static constexpr bool need_writeable = is_eigen_mutable_map<Type>::value;
+    // Delay construction (these have no default constructor)
+    std::unique_ptr<MapType> map;
+    std::unique_ptr<Type> ref;
+    // Our array.  When possible, this is just a numpy array pointing to the source data, but
+    // sometimes we can't avoid copying (e.g. input is not a numpy array at all, has an
+    // incompatible layout, or is an array of a type that needs to be converted).  Using a numpy
+    // temporary (rather than an Eigen temporary) saves an extra copy when we need both type
+    // conversion and storage order conversion.  (Note that we refuse to use this temporary copy
+    // when loading an argument for a Ref<M> with M non-const, i.e. a read-write reference).
+    Array copy_or_ref;
+
+public:
+    bool load(handle src, bool convert) {
+        // First check whether what we have is already an array of the right type.  If not, we
+        // can't avoid a copy (because the copy is also going to do type conversion).
+        bool need_copy = !isinstance<Array>(src);
+
+        EigenConformable<props::row_major> fits;
+        if (!need_copy) {
+            // We don't need a converting copy, but we also need to check whether the strides are
+            // compatible with the Ref's stride requirements
+            auto aref = reinterpret_borrow<Array>(src);
+
+            if (aref && (!need_writeable || aref.writeable())) {
+                fits = props::conformable(aref);
+                if (!fits) {
+                    return false; // Incompatible dimensions
+                }
+                if (!fits.template stride_compatible<props>()) {
+                    need_copy = true;
+                } else {
+                    copy_or_ref = std::move(aref);
+                }
+            } else {
+                need_copy = true;
+            }
+        }
+
+        if (need_copy) {
+            // We need to copy: If we need a mutable reference, or we're not supposed to convert
+            // (either because we're in the no-convert overload pass, or because we're explicitly
+            // instructed not to copy (via `py::arg().noconvert()`) we have to fail loading.
+            if (!convert || need_writeable) {
+                return false;
+            }
+
+            Array copy = Array::ensure(src);
+            if (!copy) {
+                return false;
+            }
+            fits = props::conformable(copy);
+            if (!fits || !fits.template stride_compatible<props>()) {
+                return false;
+            }
+            copy_or_ref = std::move(copy);
+            loader_life_support::add_patient(copy_or_ref);
+        }
+
+        ref.reset();
+        map.reset(new MapType(data(copy_or_ref),
+                              fits.rows,
+                              fits.cols,
+                              make_stride(fits.stride.outer(), fits.stride.inner())));
+        ref.reset(new Type(*map));
+
+        return true;
+    }
+
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator Type *() { return ref.get(); }
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator Type &() { return *ref; }
+    template <typename _T>
+    using cast_op_type = pybind11::detail::cast_op_type<_T>;
+
+private:
+    template <typename T = Type, enable_if_t<is_eigen_mutable_map<T>::value, int> = 0>
+    Scalar *data(Array &a) {
+        return a.mutable_data();
+    }
+
+    template <typename T = Type, enable_if_t<!is_eigen_mutable_map<T>::value, int> = 0>
+    const Scalar *data(Array &a) {
+        return a.data();
+    }
+
+    // Attempt to figure out a constructor of `Stride` that will work.
+    // If both strides are fixed, use a default constructor:
+    template <typename S>
+    using stride_ctor_default = bool_constant<S::InnerStrideAtCompileTime != Eigen::Dynamic
+                                              && S::OuterStrideAtCompileTime != Eigen::Dynamic
+                                              && std::is_default_constructible<S>::value>;
+    // Otherwise, if there is a two-index constructor, assume it is (outer,inner) like
+    // Eigen::Stride, and use it:
+    template <typename S>
+    using stride_ctor_dual
+        = bool_constant<!stride_ctor_default<S>::value
+                        && std::is_constructible<S, EigenIndex, EigenIndex>::value>;
+    // Otherwise, if there is a one-index constructor, and just one of the strides is dynamic, use
+    // it (passing whichever stride is dynamic).
+    template <typename S>
+    using stride_ctor_outer
+        = bool_constant<!any_of<stride_ctor_default<S>, stride_ctor_dual<S>>::value
+                        && S::OuterStrideAtCompileTime == Eigen::Dynamic
+                        && S::InnerStrideAtCompileTime != Eigen::Dynamic
+                        && std::is_constructible<S, EigenIndex>::value>;
+    template <typename S>
+    using stride_ctor_inner
+        = bool_constant<!any_of<stride_ctor_default<S>, stride_ctor_dual<S>>::value
+                        && S::InnerStrideAtCompileTime == Eigen::Dynamic
+                        && S::OuterStrideAtCompileTime != Eigen::Dynamic
+                        && std::is_constructible<S, EigenIndex>::value>;
+
+    template <typename S = StrideType, enable_if_t<stride_ctor_default<S>::value, int> = 0>
+    static S make_stride(EigenIndex, EigenIndex) {
+        return S();
+    }
+    template <typename S = StrideType, enable_if_t<stride_ctor_dual<S>::value, int> = 0>
+    static S make_stride(EigenIndex outer, EigenIndex inner) {
+        return S(outer, inner);
+    }
+    template <typename S = StrideType, enable_if_t<stride_ctor_outer<S>::value, int> = 0>
+    static S make_stride(EigenIndex outer, EigenIndex) {
+        return S(outer);
+    }
+    template <typename S = StrideType, enable_if_t<stride_ctor_inner<S>::value, int> = 0>
+    static S make_stride(EigenIndex, EigenIndex inner) {
+        return S(inner);
+    }
+};
+
+// type_caster for special matrix types (e.g. DiagonalMatrix), which are EigenBase, but not
+// EigenDense (i.e. they don't have a data(), at least not with the usual matrix layout).
+// load() is not supported, but we can cast them into the python domain by first copying to a
+// regular Eigen::Matrix, then casting that.
+template <typename Type>
+struct type_caster<Type, enable_if_t<is_eigen_other<Type>::value>> {
+    static_assert(!std::is_pointer<typename Type::Scalar>::value,
+                  PYBIND11_EIGEN_MESSAGE_POINTER_TYPES_ARE_NOT_SUPPORTED);
+
+protected:
+    using Matrix
+        = Eigen::Matrix<typename Type::Scalar, Type::RowsAtCompileTime, Type::ColsAtCompileTime>;
+    using props = EigenProps<Matrix>;
+
+public:
+    static handle cast(const Type &src, return_value_policy /* policy */, handle /* parent */) {
+        handle h = eigen_encapsulate<props>(new Matrix(src));
+        return h;
+    }
+    static handle cast(const Type *src, return_value_policy policy, handle parent) {
+        return cast(*src, policy, parent);
+    }
+
+    static constexpr auto name = props::descriptor;
+
+    // Explicitly delete these: support python -> C++ conversion on these (i.e. these can be return
+    // types but not bound arguments).  We still provide them (with an explicitly delete) so that
+    // you end up here if you try anyway.
+    bool load(handle, bool) = delete;
+    operator Type() = delete;
+    template <typename>
+    using cast_op_type = Type;
+};
+
+template <typename Type>
+struct type_caster<Type, enable_if_t<is_eigen_sparse<Type>::value>> {
+    using Scalar = typename Type::Scalar;
+    static_assert(!std::is_pointer<Scalar>::value,
+                  PYBIND11_EIGEN_MESSAGE_POINTER_TYPES_ARE_NOT_SUPPORTED);
+    using StorageIndex = remove_reference_t<decltype(*std::declval<Type>().outerIndexPtr())>;
+    using Index = typename Type::Index;
+    static constexpr bool rowMajor = Type::IsRowMajor;
+
+    bool load(handle src, bool) {
+        if (!src) {
+            return false;
+        }
+
+        auto obj = reinterpret_borrow<object>(src);
+        object sparse_module = module_::import("scipy.sparse");
+        object matrix_type = sparse_module.attr(rowMajor ? "csr_matrix" : "csc_matrix");
+
+        if (!type::handle_of(obj).is(matrix_type)) {
+            try {
+                obj = matrix_type(obj);
+            } catch (const error_already_set &) {
+                return false;
+            }
+        }
+
+        auto values = array_t<Scalar>((object) obj.attr("data"));
+        auto innerIndices = array_t<StorageIndex>((object) obj.attr("indices"));
+        auto outerIndices = array_t<StorageIndex>((object) obj.attr("indptr"));
+        auto shape = pybind11::tuple((pybind11::object) obj.attr("shape"));
+        auto nnz = obj.attr("nnz").cast<Index>();
+
+        if (!values || !innerIndices || !outerIndices) {
+            return false;
+        }
+
+        value = EigenMapSparseMatrix<Scalar,
+                                     Type::Flags &(Eigen::RowMajor | Eigen::ColMajor),
+                                     StorageIndex>(shape[0].cast<Index>(),
+                                                   shape[1].cast<Index>(),
+                                                   std::move(nnz),
+                                                   outerIndices.mutable_data(),
+                                                   innerIndices.mutable_data(),
+                                                   values.mutable_data());
+
+        return true;
+    }
+
+    static handle cast(const Type &src, return_value_policy /* policy */, handle /* parent */) {
+        const_cast<Type &>(src).makeCompressed();
+
+        object matrix_type
+            = module_::import("scipy.sparse").attr(rowMajor ? "csr_matrix" : "csc_matrix");
+
+        array data(src.nonZeros(), src.valuePtr());
+        array outerIndices((rowMajor ? src.rows() : src.cols()) + 1, src.outerIndexPtr());
+        array innerIndices(src.nonZeros(), src.innerIndexPtr());
+
+        return matrix_type(pybind11::make_tuple(
+                               std::move(data), std::move(innerIndices), std::move(outerIndices)),
+                           pybind11::make_tuple(src.rows(), src.cols()))
+            .release();
+    }
+
+    PYBIND11_TYPE_CASTER(Type,
+                         const_name<(Type::IsRowMajor) != 0>("scipy.sparse.csr_matrix[",
+                                                             "scipy.sparse.csc_matrix[")
+                             + npy_format_descriptor<Scalar>::name + const_name("]"));
+};
+
+PYBIND11_NAMESPACE_END(detail)
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
diff --git a/wrap/pybind11/include/pybind11/eigen/tensor.h b/wrap/pybind11/include/pybind11/eigen/tensor.h
new file mode 100644
index 000000000..25d12baca
--- /dev/null
+++ b/wrap/pybind11/include/pybind11/eigen/tensor.h
@@ -0,0 +1,516 @@
+/*
+    pybind11/eigen/tensor.h: Transparent conversion for Eigen tensors
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#pragma once
+
+#include "../numpy.h"
+#include "common.h"
+
+#if defined(__GNUC__) && !defined(__clang__) && !defined(__INTEL_COMPILER)
+static_assert(__GNUC__ > 5, "Eigen Tensor support in pybind11 requires GCC > 5.0");
+#endif
+
+// Disable warnings for Eigen
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_MSVC(4554)
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+#if defined(__MINGW32__)
+PYBIND11_WARNING_DISABLE_GCC("-Wmaybe-uninitialized")
+#endif
+
+#include <unsupported/Eigen/CXX11/Tensor>
+
+PYBIND11_WARNING_POP
+
+static_assert(EIGEN_VERSION_AT_LEAST(3, 3, 0),
+              "Eigen Tensor support in pybind11 requires Eigen >= 3.3.0");
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+inline bool is_tensor_aligned(const void *data) {
+    return (reinterpret_cast<std::size_t>(data) % EIGEN_DEFAULT_ALIGN_BYTES) == 0;
+}
+
+template <typename T>
+constexpr int compute_array_flag_from_tensor() {
+    static_assert((static_cast<int>(T::Layout) == static_cast<int>(Eigen::RowMajor))
+                      || (static_cast<int>(T::Layout) == static_cast<int>(Eigen::ColMajor)),
+                  "Layout must be row or column major");
+    return (static_cast<int>(T::Layout) == static_cast<int>(Eigen::RowMajor)) ? array::c_style
+                                                                              : array::f_style;
+}
+
+template <typename T>
+struct eigen_tensor_helper {};
+
+template <typename Scalar_, int NumIndices_, int Options_, typename IndexType>
+struct eigen_tensor_helper<Eigen::Tensor<Scalar_, NumIndices_, Options_, IndexType>> {
+    using Type = Eigen::Tensor<Scalar_, NumIndices_, Options_, IndexType>;
+    using ValidType = void;
+
+    static Eigen::DSizes<typename Type::Index, Type::NumIndices> get_shape(const Type &f) {
+        return f.dimensions();
+    }
+
+    static constexpr bool
+    is_correct_shape(const Eigen::DSizes<typename Type::Index, Type::NumIndices> & /*shape*/) {
+        return true;
+    }
+
+    template <typename T>
+    struct helper {};
+
+    template <size_t... Is>
+    struct helper<index_sequence<Is...>> {
+        static constexpr auto value = concat(const_name(((void) Is, "?"))...);
+    };
+
+    static constexpr auto dimensions_descriptor
+        = helper<decltype(make_index_sequence<Type::NumIndices>())>::value;
+
+    template <typename... Args>
+    static Type *alloc(Args &&...args) {
+        return new Type(std::forward<Args>(args)...);
+    }
+
+    static void free(Type *tensor) { delete tensor; }
+};
+
+template <typename Scalar_, typename std::ptrdiff_t... Indices, int Options_, typename IndexType>
+struct eigen_tensor_helper<
+    Eigen::TensorFixedSize<Scalar_, Eigen::Sizes<Indices...>, Options_, IndexType>> {
+    using Type = Eigen::TensorFixedSize<Scalar_, Eigen::Sizes<Indices...>, Options_, IndexType>;
+    using ValidType = void;
+
+    static constexpr Eigen::DSizes<typename Type::Index, Type::NumIndices>
+    get_shape(const Type & /*f*/) {
+        return get_shape();
+    }
+
+    static constexpr Eigen::DSizes<typename Type::Index, Type::NumIndices> get_shape() {
+        return Eigen::DSizes<typename Type::Index, Type::NumIndices>(Indices...);
+    }
+
+    static bool
+    is_correct_shape(const Eigen::DSizes<typename Type::Index, Type::NumIndices> &shape) {
+        return get_shape() == shape;
+    }
+
+    static constexpr auto dimensions_descriptor = concat(const_name<Indices>()...);
+
+    template <typename... Args>
+    static Type *alloc(Args &&...args) {
+        Eigen::aligned_allocator<Type> allocator;
+        return ::new (allocator.allocate(1)) Type(std::forward<Args>(args)...);
+    }
+
+    static void free(Type *tensor) {
+        Eigen::aligned_allocator<Type> allocator;
+        tensor->~Type();
+        allocator.deallocate(tensor, 1);
+    }
+};
+
+template <typename Type, bool ShowDetails, bool NeedsWriteable = false>
+struct get_tensor_descriptor {
+    static constexpr auto details
+        = const_name<NeedsWriteable>(", flags.writeable", "")
+          + const_name<static_cast<int>(Type::Layout) == static_cast<int>(Eigen::RowMajor)>(
+              ", flags.c_contiguous", ", flags.f_contiguous");
+    static constexpr auto value
+        = const_name("numpy.ndarray[") + npy_format_descriptor<typename Type::Scalar>::name
+          + const_name("[") + eigen_tensor_helper<remove_cv_t<Type>>::dimensions_descriptor
+          + const_name("]") + const_name<ShowDetails>(details, const_name("")) + const_name("]");
+};
+
+// When EIGEN_AVOID_STL_ARRAY is defined, Eigen::DSizes<T, 0> does not have the begin() member
+// function. Falling back to a simple loop works around this issue.
+//
+// We need to disable the type-limits warning for the inner loop when size = 0.
+
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_GCC("-Wtype-limits")
+
+template <typename T, int size>
+std::vector<T> convert_dsizes_to_vector(const Eigen::DSizes<T, size> &arr) {
+    std::vector<T> result(size);
+
+    for (size_t i = 0; i < size; i++) {
+        result[i] = arr[i];
+    }
+
+    return result;
+}
+
+template <typename T, int size>
+Eigen::DSizes<T, size> get_shape_for_array(const array &arr) {
+    Eigen::DSizes<T, size> result;
+    const T *shape = arr.shape();
+    for (size_t i = 0; i < size; i++) {
+        result[i] = shape[i];
+    }
+
+    return result;
+}
+
+PYBIND11_WARNING_POP
+
+template <typename Type>
+struct type_caster<Type, typename eigen_tensor_helper<Type>::ValidType> {
+    static_assert(!std::is_pointer<typename Type::Scalar>::value,
+                  PYBIND11_EIGEN_MESSAGE_POINTER_TYPES_ARE_NOT_SUPPORTED);
+    using Helper = eigen_tensor_helper<Type>;
+    static constexpr auto temp_name = get_tensor_descriptor<Type, false>::value;
+    PYBIND11_TYPE_CASTER(Type, temp_name);
+
+    bool load(handle src, bool convert) {
+        if (!convert) {
+            if (!isinstance<array>(src)) {
+                return false;
+            }
+            array temp = array::ensure(src);
+            if (!temp) {
+                return false;
+            }
+
+            if (!temp.dtype().is(dtype::of<typename Type::Scalar>())) {
+                return false;
+            }
+        }
+
+        array_t<typename Type::Scalar, compute_array_flag_from_tensor<Type>()> arr(
+            reinterpret_borrow<object>(src));
+
+        if (arr.ndim() != Type::NumIndices) {
+            return false;
+        }
+        auto shape = get_shape_for_array<typename Type::Index, Type::NumIndices>(arr);
+
+        if (!Helper::is_correct_shape(shape)) {
+            return false;
+        }
+
+#if EIGEN_VERSION_AT_LEAST(3, 4, 0)
+        auto data_pointer = arr.data();
+#else
+        // Handle Eigen bug
+        auto data_pointer = const_cast<typename Type::Scalar *>(arr.data());
+#endif
+
+        if (is_tensor_aligned(arr.data())) {
+            value = Eigen::TensorMap<const Type, Eigen::Aligned>(data_pointer, shape);
+        } else {
+            value = Eigen::TensorMap<const Type>(data_pointer, shape);
+        }
+
+        return true;
+    }
+
+    static handle cast(Type &&src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::reference
+            || policy == return_value_policy::reference_internal) {
+            pybind11_fail("Cannot use a reference return value policy for an rvalue");
+        }
+        return cast_impl(&src, return_value_policy::move, parent);
+    }
+
+    static handle cast(const Type &&src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::reference
+            || policy == return_value_policy::reference_internal) {
+            pybind11_fail("Cannot use a reference return value policy for an rvalue");
+        }
+        return cast_impl(&src, return_value_policy::move, parent);
+    }
+
+    static handle cast(Type &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic
+            || policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::copy;
+        }
+        return cast_impl(&src, policy, parent);
+    }
+
+    static handle cast(const Type &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic
+            || policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::copy;
+        }
+        return cast(&src, policy, parent);
+    }
+
+    static handle cast(Type *src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic) {
+            policy = return_value_policy::take_ownership;
+        } else if (policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::reference;
+        }
+        return cast_impl(src, policy, parent);
+    }
+
+    static handle cast(const Type *src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic) {
+            policy = return_value_policy::take_ownership;
+        } else if (policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::reference;
+        }
+        return cast_impl(src, policy, parent);
+    }
+
+    template <typename C>
+    static handle cast_impl(C *src, return_value_policy policy, handle parent) {
+        object parent_object;
+        bool writeable = false;
+        switch (policy) {
+            case return_value_policy::move:
+                if (std::is_const<C>::value) {
+                    pybind11_fail("Cannot move from a constant reference");
+                }
+
+                src = Helper::alloc(std::move(*src));
+
+                parent_object
+                    = capsule(src, [](void *ptr) { Helper::free(reinterpret_cast<Type *>(ptr)); });
+                writeable = true;
+                break;
+
+            case return_value_policy::take_ownership:
+                if (std::is_const<C>::value) {
+                    // This cast is ugly, and might be UB in some cases, but we don't have an
+                    // alternative here as we must free that memory
+                    Helper::free(const_cast<Type *>(src));
+                    pybind11_fail("Cannot take ownership of a const reference");
+                }
+
+                parent_object
+                    = capsule(src, [](void *ptr) { Helper::free(reinterpret_cast<Type *>(ptr)); });
+                writeable = true;
+                break;
+
+            case return_value_policy::copy:
+                writeable = true;
+                break;
+
+            case return_value_policy::reference:
+                parent_object = none();
+                writeable = !std::is_const<C>::value;
+                break;
+
+            case return_value_policy::reference_internal:
+                // Default should do the right thing
+                if (!parent) {
+                    pybind11_fail("Cannot use reference internal when there is no parent");
+                }
+                parent_object = reinterpret_borrow<object>(parent);
+                writeable = !std::is_const<C>::value;
+                break;
+
+            default:
+                pybind11_fail("pybind11 bug in eigen.h, please file a bug report");
+        }
+
+        auto result = array_t<typename Type::Scalar, compute_array_flag_from_tensor<Type>()>(
+            convert_dsizes_to_vector(Helper::get_shape(*src)), src->data(), parent_object);
+
+        if (!writeable) {
+            array_proxy(result.ptr())->flags &= ~detail::npy_api::NPY_ARRAY_WRITEABLE_;
+        }
+
+        return result.release();
+    }
+};
+
+template <typename StoragePointerType,
+          bool needs_writeable,
+          enable_if_t<!needs_writeable, bool> = true>
+StoragePointerType get_array_data_for_type(array &arr) {
+#if EIGEN_VERSION_AT_LEAST(3, 4, 0)
+    return reinterpret_cast<StoragePointerType>(arr.data());
+#else
+    // Handle Eigen bug
+    return reinterpret_cast<StoragePointerType>(const_cast<void *>(arr.data()));
+#endif
+}
+
+template <typename StoragePointerType,
+          bool needs_writeable,
+          enable_if_t<needs_writeable, bool> = true>
+StoragePointerType get_array_data_for_type(array &arr) {
+    return reinterpret_cast<StoragePointerType>(arr.mutable_data());
+}
+
+template <typename T, typename = void>
+struct get_storage_pointer_type;
+
+template <typename MapType>
+struct get_storage_pointer_type<MapType, void_t<typename MapType::StoragePointerType>> {
+    using SPT = typename MapType::StoragePointerType;
+};
+
+template <typename MapType>
+struct get_storage_pointer_type<MapType, void_t<typename MapType::PointerArgType>> {
+    using SPT = typename MapType::PointerArgType;
+};
+
+template <typename Type, int Options>
+struct type_caster<Eigen::TensorMap<Type, Options>,
+                   typename eigen_tensor_helper<remove_cv_t<Type>>::ValidType> {
+    static_assert(!std::is_pointer<typename Type::Scalar>::value,
+                  PYBIND11_EIGEN_MESSAGE_POINTER_TYPES_ARE_NOT_SUPPORTED);
+    using MapType = Eigen::TensorMap<Type, Options>;
+    using Helper = eigen_tensor_helper<remove_cv_t<Type>>;
+
+    bool load(handle src, bool /*convert*/) {
+        // Note that we have a lot more checks here as we want to make sure to avoid copies
+        if (!isinstance<array>(src)) {
+            return false;
+        }
+        auto arr = reinterpret_borrow<array>(src);
+        if ((arr.flags() & compute_array_flag_from_tensor<Type>()) == 0) {
+            return false;
+        }
+
+        if (!arr.dtype().is(dtype::of<typename Type::Scalar>())) {
+            return false;
+        }
+
+        if (arr.ndim() != Type::NumIndices) {
+            return false;
+        }
+
+        constexpr bool is_aligned = (Options & Eigen::Aligned) != 0;
+
+        if (is_aligned && !is_tensor_aligned(arr.data())) {
+            return false;
+        }
+
+        auto shape = get_shape_for_array<typename Type::Index, Type::NumIndices>(arr);
+
+        if (!Helper::is_correct_shape(shape)) {
+            return false;
+        }
+
+        if (needs_writeable && !arr.writeable()) {
+            return false;
+        }
+
+        auto result = get_array_data_for_type<typename get_storage_pointer_type<MapType>::SPT,
+                                              needs_writeable>(arr);
+
+        value.reset(new MapType(std::move(result), std::move(shape)));
+
+        return true;
+    }
+
+    static handle cast(MapType &&src, return_value_policy policy, handle parent) {
+        return cast_impl(&src, policy, parent);
+    }
+
+    static handle cast(const MapType &&src, return_value_policy policy, handle parent) {
+        return cast_impl(&src, policy, parent);
+    }
+
+    static handle cast(MapType &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic
+            || policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::copy;
+        }
+        return cast_impl(&src, policy, parent);
+    }
+
+    static handle cast(const MapType &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic
+            || policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::copy;
+        }
+        return cast(&src, policy, parent);
+    }
+
+    static handle cast(MapType *src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic) {
+            policy = return_value_policy::take_ownership;
+        } else if (policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::reference;
+        }
+        return cast_impl(src, policy, parent);
+    }
+
+    static handle cast(const MapType *src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic) {
+            policy = return_value_policy::take_ownership;
+        } else if (policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::reference;
+        }
+        return cast_impl(src, policy, parent);
+    }
+
+    template <typename C>
+    static handle cast_impl(C *src, return_value_policy policy, handle parent) {
+        object parent_object;
+        constexpr bool writeable = !std::is_const<C>::value;
+        switch (policy) {
+            case return_value_policy::reference:
+                parent_object = none();
+                break;
+
+            case return_value_policy::reference_internal:
+                // Default should do the right thing
+                if (!parent) {
+                    pybind11_fail("Cannot use reference internal when there is no parent");
+                }
+                parent_object = reinterpret_borrow<object>(parent);
+                break;
+
+            case return_value_policy::take_ownership:
+                delete src;
+                // fallthrough
+            default:
+                // move, take_ownership don't make any sense for a ref/map:
+                pybind11_fail("Invalid return_value_policy for Eigen Map type, must be either "
+                              "reference or reference_internal");
+        }
+
+        auto result = array_t<typename Type::Scalar, compute_array_flag_from_tensor<Type>()>(
+            convert_dsizes_to_vector(Helper::get_shape(*src)),
+            src->data(),
+            std::move(parent_object));
+
+        if (!writeable) {
+            array_proxy(result.ptr())->flags &= ~detail::npy_api::NPY_ARRAY_WRITEABLE_;
+        }
+
+        return result.release();
+    }
+
+#if EIGEN_VERSION_AT_LEAST(3, 4, 0)
+
+    static constexpr bool needs_writeable = !std::is_const<typename std::remove_pointer<
+        typename get_storage_pointer_type<MapType>::SPT>::type>::value;
+#else
+    // Handle Eigen bug
+    static constexpr bool needs_writeable = !std::is_const<Type>::value;
+#endif
+
+protected:
+    // TODO: Move to std::optional once std::optional has more support
+    std::unique_ptr<MapType> value;
+
+public:
+    static constexpr auto name = get_tensor_descriptor<Type, true, needs_writeable>::value;
+    explicit operator MapType *() { return value.get(); }
+    explicit operator MapType &() { return *value; }
+    explicit operator MapType &&() && { return std::move(*value); }
+
+    template <typename T_>
+    using cast_op_type = ::pybind11::detail::movable_cast_op_type<T_>;
+};
+
+PYBIND11_NAMESPACE_END(detail)
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
diff --git a/wrap/pybind11/include/pybind11/embed.h b/wrap/pybind11/include/pybind11/embed.h
index d6999cd77..caa14f4a0 100644
--- a/wrap/pybind11/include/pybind11/embed.h
+++ b/wrap/pybind11/include/pybind11/embed.h
@@ -86,38 +86,26 @@ inline wchar_t *widen_chars(const char *safe_arg) {
     return widened_arg;
 }
 
-PYBIND11_NAMESPACE_END(detail)
-
-/** \rst
-    Initialize the Python interpreter. No other pybind11 or CPython API functions can be
-    called before this is done; with the exception of `PYBIND11_EMBEDDED_MODULE`. The
-    optional `init_signal_handlers` parameter can be used to skip the registration of
-    signal handlers (see the `Python documentation`_ for details). Calling this function
-    again after the interpreter has already been initialized is a fatal error.
-
-    If initializing the Python interpreter fails, then the program is terminated.  (This
-    is controlled by the CPython runtime and is an exception to pybind11's normal behavior
-    of throwing exceptions on errors.)
-
-    The remaining optional parameters, `argc`, `argv`, and `add_program_dir_to_path` are
-    used to populate ``sys.argv`` and ``sys.path``.
-    See the |PySys_SetArgvEx documentation|_ for details.
-
-    .. _Python documentation: https://docs.python.org/3/c-api/init.html#c.Py_InitializeEx
-    .. |PySys_SetArgvEx documentation| replace:: ``PySys_SetArgvEx`` documentation
-    .. _PySys_SetArgvEx documentation: https://docs.python.org/3/c-api/init.html#c.PySys_SetArgvEx
- \endrst */
-inline void initialize_interpreter(bool init_signal_handlers = true,
-                                   int argc = 0,
-                                   const char *const *argv = nullptr,
-                                   bool add_program_dir_to_path = true) {
+inline void precheck_interpreter() {
     if (Py_IsInitialized() != 0) {
         pybind11_fail("The interpreter is already running");
     }
+}
 
-#if PY_VERSION_HEX < 0x030B0000
+#if !defined(PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX)
+#    define PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX (0x03080000)
+#endif
 
+#if PY_VERSION_HEX < PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX
+inline void initialize_interpreter_pre_pyconfig(bool init_signal_handlers,
+                                                int argc,
+                                                const char *const *argv,
+                                                bool add_program_dir_to_path) {
+    detail::precheck_interpreter();
     Py_InitializeEx(init_signal_handlers ? 1 : 0);
+#    if defined(WITH_THREAD) && PY_VERSION_HEX < 0x03070000
+    PyEval_InitThreads();
+#    endif
 
     // Before it was special-cased in python 3.8, passing an empty or null argv
     // caused a segfault, so we have to reimplement the special case ourselves.
@@ -147,24 +135,30 @@ inline void initialize_interpreter(bool init_signal_handlers = true,
     auto *pysys_argv = widened_argv.get();
 
     PySys_SetArgvEx(argc, pysys_argv, static_cast<int>(add_program_dir_to_path));
-#else
-    PyConfig config;
-    PyConfig_InitIsolatedConfig(&config);
-    config.install_signal_handlers = init_signal_handlers ? 1 : 0;
+}
+#endif
 
-    PyStatus status = PyConfig_SetBytesArgv(&config, argc, const_cast<char *const *>(argv));
-    if (PyStatus_Exception(status)) {
+PYBIND11_NAMESPACE_END(detail)
+
+#if PY_VERSION_HEX >= PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX
+inline void initialize_interpreter(PyConfig *config,
+                                   int argc = 0,
+                                   const char *const *argv = nullptr,
+                                   bool add_program_dir_to_path = true) {
+    detail::precheck_interpreter();
+    PyStatus status = PyConfig_SetBytesArgv(config, argc, const_cast<char *const *>(argv));
+    if (PyStatus_Exception(status) != 0) {
         // A failure here indicates a character-encoding failure or the python
         // interpreter out of memory. Give up.
-        PyConfig_Clear(&config);
-        throw std::runtime_error(PyStatus_IsError(status) ? status.err_msg
-                                                          : "Failed to prepare CPython");
+        PyConfig_Clear(config);
+        throw std::runtime_error(PyStatus_IsError(status) != 0 ? status.err_msg
+                                                               : "Failed to prepare CPython");
     }
-    status = Py_InitializeFromConfig(&config);
-    PyConfig_Clear(&config);
-    if (PyStatus_Exception(status)) {
-        throw std::runtime_error(PyStatus_IsError(status) ? status.err_msg
-                                                          : "Failed to init CPython");
+    status = Py_InitializeFromConfig(config);
+    if (PyStatus_Exception(status) != 0) {
+        PyConfig_Clear(config);
+        throw std::runtime_error(PyStatus_IsError(status) != 0 ? status.err_msg
+                                                               : "Failed to init CPython");
     }
     if (add_program_dir_to_path) {
         PyRun_SimpleString("import sys, os.path; "
@@ -172,6 +166,44 @@ inline void initialize_interpreter(bool init_signal_handlers = true,
                            "os.path.abspath(os.path.dirname(sys.argv[0])) "
                            "if sys.argv and os.path.exists(sys.argv[0]) else '')");
     }
+    PyConfig_Clear(config);
+}
+#endif
+
+/** \rst
+    Initialize the Python interpreter. No other pybind11 or CPython API functions can be
+    called before this is done; with the exception of `PYBIND11_EMBEDDED_MODULE`. The
+    optional `init_signal_handlers` parameter can be used to skip the registration of
+    signal handlers (see the `Python documentation`_ for details). Calling this function
+    again after the interpreter has already been initialized is a fatal error.
+
+    If initializing the Python interpreter fails, then the program is terminated.  (This
+    is controlled by the CPython runtime and is an exception to pybind11's normal behavior
+    of throwing exceptions on errors.)
+
+    The remaining optional parameters, `argc`, `argv`, and `add_program_dir_to_path` are
+    used to populate ``sys.argv`` and ``sys.path``.
+    See the |PySys_SetArgvEx documentation|_ for details.
+
+    .. _Python documentation: https://docs.python.org/3/c-api/init.html#c.Py_InitializeEx
+    .. |PySys_SetArgvEx documentation| replace:: ``PySys_SetArgvEx`` documentation
+    .. _PySys_SetArgvEx documentation: https://docs.python.org/3/c-api/init.html#c.PySys_SetArgvEx
+ \endrst */
+inline void initialize_interpreter(bool init_signal_handlers = true,
+                                   int argc = 0,
+                                   const char *const *argv = nullptr,
+                                   bool add_program_dir_to_path = true) {
+#if PY_VERSION_HEX < PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX
+    detail::initialize_interpreter_pre_pyconfig(
+        init_signal_handlers, argc, argv, add_program_dir_to_path);
+#else
+    PyConfig config;
+    PyConfig_InitPythonConfig(&config);
+    // See PR #4473 for background
+    config.parse_argv = 0;
+
+    config.install_signal_handlers = init_signal_handlers ? 1 : 0;
+    initialize_interpreter(&config, argc, argv, add_program_dir_to_path);
 #endif
 }
 
@@ -211,16 +243,14 @@ inline void initialize_interpreter(bool init_signal_handlers = true,
 
  \endrst */
 inline void finalize_interpreter() {
-    handle builtins(PyEval_GetBuiltins());
-    const char *id = PYBIND11_INTERNALS_ID;
-
     // Get the internals pointer (without creating it if it doesn't exist).  It's possible for the
     // internals to be created during Py_Finalize() (e.g. if a py::capsule calls `get_internals()`
     // during destruction), so we get the pointer-pointer here and check it after Py_Finalize().
     detail::internals **internals_ptr_ptr = detail::get_internals_pp();
-    // It could also be stashed in builtins, so look there too:
-    if (builtins.contains(id) && isinstance<capsule>(builtins[id])) {
-        internals_ptr_ptr = capsule(builtins[id]);
+    // It could also be stashed in state_dict, so look there too:
+    if (object internals_obj
+        = get_internals_obj_from_state_dict(detail::get_python_state_dict())) {
+        internals_ptr_ptr = detail::get_internals_pp_from_capsule(internals_obj);
     }
     // Local internals contains data managed by the current interpreter, so we must clear them to
     // avoid undefined behaviors when initializing another interpreter
@@ -259,6 +289,15 @@ public:
         initialize_interpreter(init_signal_handlers, argc, argv, add_program_dir_to_path);
     }
 
+#if PY_VERSION_HEX >= PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX
+    explicit scoped_interpreter(PyConfig *config,
+                                int argc = 0,
+                                const char *const *argv = nullptr,
+                                bool add_program_dir_to_path = true) {
+        initialize_interpreter(config, argc, argv, add_program_dir_to_path);
+    }
+#endif
+
     scoped_interpreter(const scoped_interpreter &) = delete;
     scoped_interpreter(scoped_interpreter &&other) noexcept { other.is_valid = false; }
     scoped_interpreter &operator=(const scoped_interpreter &) = delete;
diff --git a/wrap/pybind11/include/pybind11/functional.h b/wrap/pybind11/include/pybind11/functional.h
index 4034990d8..87ec4d10c 100644
--- a/wrap/pybind11/include/pybind11/functional.h
+++ b/wrap/pybind11/include/pybind11/functional.h
@@ -48,9 +48,16 @@ public:
          */
         if (auto cfunc = func.cpp_function()) {
             auto *cfunc_self = PyCFunction_GET_SELF(cfunc.ptr());
-            if (isinstance<capsule>(cfunc_self)) {
+            if (cfunc_self == nullptr) {
+                PyErr_Clear();
+            } else if (isinstance<capsule>(cfunc_self)) {
                 auto c = reinterpret_borrow<capsule>(cfunc_self);
-                auto *rec = (function_record *) c;
+
+                function_record *rec = nullptr;
+                // Check that we can safely reinterpret the capsule into a function_record
+                if (detail::is_function_record_capsule(c)) {
+                    rec = c.get_pointer<function_record>();
+                }
 
                 while (rec != nullptr) {
                     if (rec->is_stateless
@@ -110,7 +117,7 @@ public:
     template <typename Func>
     static handle cast(Func &&f_, return_value_policy policy, handle /* parent */) {
         if (!f_) {
-            return none().inc_ref();
+            return none().release();
         }
 
         auto result = f_.template target<function_type>();
diff --git a/wrap/pybind11/include/pybind11/gil.h b/wrap/pybind11/include/pybind11/gil.h
index a0b5de151..570a5581d 100644
--- a/wrap/pybind11/include/pybind11/gil.h
+++ b/wrap/pybind11/include/pybind11/gil.h
@@ -10,7 +10,10 @@
 #pragma once
 
 #include "detail/common.h"
-#include "detail/internals.h"
+
+#if defined(WITH_THREAD) && !defined(PYBIND11_SIMPLE_GIL_MANAGEMENT)
+#    include "detail/internals.h"
+#endif
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
@@ -21,7 +24,9 @@ PyThreadState *get_thread_state_unchecked();
 
 PYBIND11_NAMESPACE_END(detail)
 
-#if defined(WITH_THREAD) && !defined(PYPY_VERSION)
+#if defined(WITH_THREAD)
+
+#    if !defined(PYBIND11_SIMPLE_GIL_MANAGEMENT)
 
 /* The functions below essentially reproduce the PyGILState_* API using a RAII
  * pattern, but there are a few important differences:
@@ -62,11 +67,11 @@ public:
 
         if (!tstate) {
             tstate = PyThreadState_New(internals.istate);
-#    if defined(PYBIND11_DETAILED_ERROR_MESSAGES)
+#        if defined(PYBIND11_DETAILED_ERROR_MESSAGES)
             if (!tstate) {
                 pybind11_fail("scoped_acquire: could not create thread state!");
             }
-#    endif
+#        endif
             tstate->gilstate_counter = 0;
             PYBIND11_TLS_REPLACE_VALUE(internals.tstate, tstate);
         } else {
@@ -80,24 +85,27 @@ public:
         inc_ref();
     }
 
+    gil_scoped_acquire(const gil_scoped_acquire &) = delete;
+    gil_scoped_acquire &operator=(const gil_scoped_acquire &) = delete;
+
     void inc_ref() { ++tstate->gilstate_counter; }
 
     PYBIND11_NOINLINE void dec_ref() {
         --tstate->gilstate_counter;
-#    if defined(PYBIND11_DETAILED_ERROR_MESSAGES)
+#        if defined(PYBIND11_DETAILED_ERROR_MESSAGES)
         if (detail::get_thread_state_unchecked() != tstate) {
             pybind11_fail("scoped_acquire::dec_ref(): thread state must be current!");
         }
         if (tstate->gilstate_counter < 0) {
             pybind11_fail("scoped_acquire::dec_ref(): reference count underflow!");
         }
-#    endif
+#        endif
         if (tstate->gilstate_counter == 0) {
-#    if defined(PYBIND11_DETAILED_ERROR_MESSAGES)
+#        if defined(PYBIND11_DETAILED_ERROR_MESSAGES)
             if (!release) {
                 pybind11_fail("scoped_acquire::dec_ref(): internal error!");
             }
-#    endif
+#        endif
             PyThreadState_Clear(tstate);
             if (active) {
                 PyThreadState_DeleteCurrent();
@@ -144,6 +152,9 @@ public:
         }
     }
 
+    gil_scoped_release(const gil_scoped_release &) = delete;
+    gil_scoped_release &operator=(const gil_scoped_release &) = delete;
+
     /// This method will disable the PyThreadState_DeleteCurrent call and the
     /// GIL won't be acquired. This method should be used if the interpreter
     /// could be shutting down when this is called, as thread deletion is not
@@ -172,12 +183,16 @@ private:
     bool disassoc;
     bool active = true;
 };
-#elif defined(PYPY_VERSION)
+
+#    else // PYBIND11_SIMPLE_GIL_MANAGEMENT
+
 class gil_scoped_acquire {
     PyGILState_STATE state;
 
 public:
-    gil_scoped_acquire() { state = PyGILState_Ensure(); }
+    gil_scoped_acquire() : state{PyGILState_Ensure()} {}
+    gil_scoped_acquire(const gil_scoped_acquire &) = delete;
+    gil_scoped_acquire &operator=(const gil_scoped_acquire &) = delete;
     ~gil_scoped_acquire() { PyGILState_Release(state); }
     void disarm() {}
 };
@@ -186,17 +201,39 @@ class gil_scoped_release {
     PyThreadState *state;
 
 public:
-    gil_scoped_release() { state = PyEval_SaveThread(); }
+    gil_scoped_release() : state{PyEval_SaveThread()} {}
+    gil_scoped_release(const gil_scoped_release &) = delete;
+    gil_scoped_release &operator=(const gil_scoped_release &) = delete;
     ~gil_scoped_release() { PyEval_RestoreThread(state); }
     void disarm() {}
 };
-#else
+
+#    endif // PYBIND11_SIMPLE_GIL_MANAGEMENT
+
+#else // WITH_THREAD
+
 class gil_scoped_acquire {
+public:
+    gil_scoped_acquire() {
+        // Trick to suppress `unused variable` error messages (at call sites).
+        (void) (this != (this + 1));
+    }
+    gil_scoped_acquire(const gil_scoped_acquire &) = delete;
+    gil_scoped_acquire &operator=(const gil_scoped_acquire &) = delete;
     void disarm() {}
 };
+
 class gil_scoped_release {
+public:
+    gil_scoped_release() {
+        // Trick to suppress `unused variable` error messages (at call sites).
+        (void) (this != (this + 1));
+    }
+    gil_scoped_release(const gil_scoped_release &) = delete;
+    gil_scoped_release &operator=(const gil_scoped_release &) = delete;
     void disarm() {}
 };
-#endif
+
+#endif // WITH_THREAD
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
diff --git a/wrap/pybind11/include/pybind11/numpy.h b/wrap/pybind11/include/pybind11/numpy.h
index 0291b02d0..36077ec04 100644
--- a/wrap/pybind11/include/pybind11/numpy.h
+++ b/wrap/pybind11/include/pybind11/numpy.h
@@ -36,6 +36,8 @@ static_assert(std::is_signed<Py_intptr_t>::value, "Py_intptr_t must be signed");
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
 class array; // Forward declaration
 
 PYBIND11_NAMESPACE_BEGIN(detail)
@@ -537,7 +539,7 @@ PYBIND11_NAMESPACE_END(detail)
 
 class dtype : public object {
 public:
-    PYBIND11_OBJECT_DEFAULT(dtype, object, detail::npy_api::get().PyArrayDescr_Check_);
+    PYBIND11_OBJECT_DEFAULT(dtype, object, detail::npy_api::get().PyArrayDescr_Check_)
 
     explicit dtype(const buffer_info &info) {
         dtype descr(_dtype_from_pep3118()(pybind11::str(info.format)));
@@ -562,6 +564,8 @@ public:
         m_ptr = from_args(args).release().ptr();
     }
 
+    /// Return dtype for the given typenum (one of the NPY_TYPES).
+    /// https://numpy.org/devdocs/reference/c-api/array.html#c.PyArray_DescrFromType
     explicit dtype(int typenum)
         : object(detail::npy_api::get().PyArray_DescrFromType_(typenum), stolen_t{}) {
         if (m_ptr == nullptr) {
@@ -875,7 +879,7 @@ public:
      */
     template <typename T, ssize_t Dims = -1>
     detail::unchecked_mutable_reference<T, Dims> mutable_unchecked() & {
-        if (PYBIND11_SILENCE_MSVC_C4127(Dims >= 0) && ndim() != Dims) {
+        if (Dims >= 0 && ndim() != Dims) {
             throw std::domain_error("array has incorrect number of dimensions: "
                                     + std::to_string(ndim()) + "; expected "
                                     + std::to_string(Dims));
@@ -893,7 +897,7 @@ public:
      */
     template <typename T, ssize_t Dims = -1>
     detail::unchecked_reference<T, Dims> unchecked() const & {
-        if (PYBIND11_SILENCE_MSVC_C4127(Dims >= 0) && ndim() != Dims) {
+        if (Dims >= 0 && ndim() != Dims) {
             throw std::domain_error("array has incorrect number of dimensions: "
                                     + std::to_string(ndim()) + "; expected "
                                     + std::to_string(Dims));
@@ -1119,10 +1123,10 @@ public:
 
     /**
      * Returns a proxy object that provides const access to the array's data without bounds or
-     * dimensionality checking.  Unlike `unchecked()`, this does not require that the underlying
-     * array have the `writable` flag.  Use with care: the array must not be destroyed or reshaped
-     * for the duration of the returned object, and the caller must take care not to access invalid
-     * dimensions or dimension indices.
+     * dimensionality checking.  Unlike `mutable_unchecked()`, this does not require that the
+     * underlying array have the `writable` flag.  Use with care: the array must not be destroyed
+     * or reshaped for the duration of the returned object, and the caller must take care not to
+     * access invalid dimensions or dimension indices.
      */
     template <ssize_t Dims = -1>
     detail::unchecked_reference<T, Dims> unchecked() const & {
@@ -1281,12 +1285,16 @@ private:
 public:
     static constexpr int value = values[detail::is_fmt_numeric<T>::index];
 
-    static pybind11::dtype dtype() {
-        if (auto *ptr = npy_api::get().PyArray_DescrFromType_(value)) {
-            return reinterpret_steal<pybind11::dtype>(ptr);
-        }
-        pybind11_fail("Unsupported buffer format!");
-    }
+    static pybind11::dtype dtype() { return pybind11::dtype(/*typenum*/ value); }
+};
+
+template <typename T>
+struct npy_format_descriptor<T, enable_if_t<is_same_ignoring_cvref<T, PyObject *>::value>> {
+    static constexpr auto name = const_name("object");
+
+    static constexpr int value = npy_api::NPY_OBJECT_;
+
+    static pybind11::dtype dtype() { return pybind11::dtype(/*typenum*/ value); }
 };
 
 #define PYBIND11_DECL_CHAR_FMT                                                                    \
@@ -1401,7 +1409,7 @@ PYBIND11_NOINLINE void register_structured_dtype(any_container<field_descriptor>
     oss << '}';
     auto format_str = oss.str();
 
-    // Sanity check: verify that NumPy properly parses our buffer format string
+    // Smoke test: verify that NumPy properly parses our buffer format string
     auto &api = npy_api::get();
     auto arr = array(buffer_info(nullptr, itemsize, format_str, 1));
     if (!api.PyArray_EquivTypes_(dtype_ptr, arr.dtype().ptr())) {
@@ -1469,7 +1477,7 @@ private:
         }
 
 // Extract name, offset and format descriptor for a struct field
-#    define PYBIND11_FIELD_DESCRIPTOR(T, Field) PYBIND11_FIELD_DESCRIPTOR_EX(T, Field, #    Field)
+#    define PYBIND11_FIELD_DESCRIPTOR(T, Field) PYBIND11_FIELD_DESCRIPTOR_EX(T, Field, #Field)
 
 // The main idea of this macro is borrowed from https://github.com/swansontec/map-macro
 // (C) William Swanson, Paul Fultz
@@ -1866,8 +1874,13 @@ private:
 
         auto result = returned_array::create(trivial, shape);
 
+        PYBIND11_WARNING_PUSH
+#ifdef PYBIND11_DETECTED_CLANG_WITH_MISLEADING_CALL_STD_MOVE_EXPLICITLY_WARNING
+        PYBIND11_WARNING_DISABLE_CLANG("-Wreturn-std-move")
+#endif
+
         if (size == 0) {
-            return std::move(result);
+            return result;
         }
 
         /* Call the function */
@@ -1878,7 +1891,8 @@ private:
             apply_trivial(buffers, params, mutable_data, size, i_seq, vi_seq, bi_seq);
         }
 
-        return std::move(result);
+        return result;
+        PYBIND11_WARNING_POP
     }
 
     template <size_t... Index, size_t... VIndex, size_t... BIndex>
diff --git a/wrap/pybind11/include/pybind11/operators.h b/wrap/pybind11/include/pybind11/operators.h
index a0c3b78d6..16a88ae17 100644
--- a/wrap/pybind11/include/pybind11/operators.h
+++ b/wrap/pybind11/include/pybind11/operators.h
@@ -84,6 +84,7 @@ struct op_impl {};
 /// Operator implementation generator
 template <op_id id, op_type ot, typename L, typename R>
 struct op_ {
+    static constexpr bool op_enable_if_hook = true;
     template <typename Class, typename... Extra>
     void execute(Class &cl, const Extra &...extra) const {
         using Base = typename Class::type;
diff --git a/wrap/pybind11/include/pybind11/options.h b/wrap/pybind11/include/pybind11/options.h
index 1e493bdcc..1b2122522 100644
--- a/wrap/pybind11/include/pybind11/options.h
+++ b/wrap/pybind11/include/pybind11/options.h
@@ -47,6 +47,16 @@ public:
         return *this;
     }
 
+    options &disable_enum_members_docstring() & {
+        global_state().show_enum_members_docstring = false;
+        return *this;
+    }
+
+    options &enable_enum_members_docstring() & {
+        global_state().show_enum_members_docstring = true;
+        return *this;
+    }
+
     // Getter methods (return the global state):
 
     static bool show_user_defined_docstrings() {
@@ -55,6 +65,10 @@ public:
 
     static bool show_function_signatures() { return global_state().show_function_signatures; }
 
+    static bool show_enum_members_docstring() {
+        return global_state().show_enum_members_docstring;
+    }
+
     // This type is not meant to be allocated on the heap.
     void *operator new(size_t) = delete;
 
@@ -63,6 +77,8 @@ private:
         bool show_user_defined_docstrings = true; //< Include user-supplied texts in docstrings.
         bool show_function_signatures = true;     //< Include auto-generated function signatures
                                                   //  in docstrings.
+        bool show_enum_members_docstring = true;  //< Include auto-generated member list in enum
+                                                  //  docstrings.
     };
 
     static state &global_state() {
diff --git a/wrap/pybind11/include/pybind11/pybind11.h b/wrap/pybind11/include/pybind11/pybind11.h
index d61dcd5c7..3bce1a01b 100644
--- a/wrap/pybind11/include/pybind11/pybind11.h
+++ b/wrap/pybind11/include/pybind11/pybind11.h
@@ -35,6 +35,8 @@
 #    include <cxxabi.h>
 #endif
 
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
 /* https://stackoverflow.com/questions/46798456/handling-gccs-noexcept-type-warning
    This warning is about ABI compatibility, not code health.
    It is only actually needed in a couple places, but apparently GCC 7 "generates this warning if
@@ -43,11 +45,10 @@
    No other GCC version generates this warning.
  */
 #if defined(__GNUC__) && __GNUC__ == 7
-#    pragma GCC diagnostic push
-#    pragma GCC diagnostic ignored "-Wnoexcept-type"
+PYBIND11_WARNING_DISABLE_GCC("-Wnoexcept-type")
 #endif
 
-PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+PYBIND11_WARNING_DISABLE_MSVC(4127)
 
 PYBIND11_NAMESPACE_BEGIN(detail)
 
@@ -83,6 +84,7 @@ public:
     cpp_function() = default;
     // NOLINTNEXTLINE(google-explicit-constructor)
     cpp_function(std::nullptr_t) {}
+    cpp_function(std::nullptr_t, const is_setter &) {}
 
     /// Construct a cpp_function from a vanilla function pointer
     template <typename Return, typename... Args, typename... Extra>
@@ -177,22 +179,22 @@ protected:
         auto *rec = unique_rec.get();
 
         /* Store the capture object directly in the function record if there is enough space */
-        if (PYBIND11_SILENCE_MSVC_C4127(sizeof(capture) <= sizeof(rec->data))) {
+        if (sizeof(capture) <= sizeof(rec->data)) {
             /* Without these pragmas, GCC warns that there might not be
                enough space to use the placement new operator. However, the
                'if' statement above ensures that this is the case. */
-#if defined(__GNUG__) && __GNUC__ >= 6 && !defined(__clang__) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic push
-#    pragma GCC diagnostic ignored "-Wplacement-new"
+            PYBIND11_WARNING_PUSH
+
+#if defined(__GNUG__) && __GNUC__ >= 6
+            PYBIND11_WARNING_DISABLE_GCC("-Wplacement-new")
 #endif
+
             new ((capture *) &rec->data) capture{std::forward<Func>(f)};
-#if defined(__GNUG__) && __GNUC__ >= 6 && !defined(__clang__) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic pop
-#endif
-#if defined(__GNUG__) && !PYBIND11_HAS_STD_LAUNDER && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic push
-#    pragma GCC diagnostic ignored "-Wstrict-aliasing"
+
+#if !PYBIND11_HAS_STD_LAUNDER
+            PYBIND11_WARNING_DISABLE_GCC("-Wstrict-aliasing")
 #endif
+
             // UB without std::launder, but without breaking ABI and/or
             // a significant refactoring it's "impossible" to solve.
             if (!std::is_trivially_destructible<capture>::value) {
@@ -202,9 +204,7 @@ protected:
                     data->~capture();
                 };
             }
-#if defined(__GNUG__) && !PYBIND11_HAS_STD_LAUNDER && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic pop
-#endif
+            PYBIND11_WARNING_POP
         } else {
             rec->data[0] = new capture{std::forward<Func>(f)};
             rec->free_data = [](function_record *r) { delete ((capture *) r->data[0]); };
@@ -245,10 +245,16 @@ protected:
             using Guard = extract_guard_t<Extra...>;
 
             /* Perform the function call */
-            handle result
-                = cast_out::cast(std::move(args_converter).template call<Return, Guard>(cap->f),
-                                 policy,
-                                 call.parent);
+            handle result;
+            if (call.func.is_setter) {
+                (void) std::move(args_converter).template call<Return, Guard>(cap->f);
+                result = none().release();
+            } else {
+                result = cast_out::cast(
+                    std::move(args_converter).template call<Return, Guard>(cap->f),
+                    policy,
+                    call.parent);
+            }
 
             /* Invoke call policy post-call hook */
             process_attributes<Extra...>::postcall(call, result);
@@ -468,13 +474,20 @@ protected:
         if (rec->sibling) {
             if (PyCFunction_Check(rec->sibling.ptr())) {
                 auto *self = PyCFunction_GET_SELF(rec->sibling.ptr());
-                capsule rec_capsule = isinstance<capsule>(self) ? reinterpret_borrow<capsule>(self)
-                                                                : capsule(self);
-                chain = (detail::function_record *) rec_capsule;
-                /* Never append a method to an overload chain of a parent class;
-                   instead, hide the parent's overloads in this case */
-                if (!chain->scope.is(rec->scope)) {
+                if (!isinstance<capsule>(self)) {
                     chain = nullptr;
+                } else {
+                    auto rec_capsule = reinterpret_borrow<capsule>(self);
+                    if (detail::is_function_record_capsule(rec_capsule)) {
+                        chain = rec_capsule.get_pointer<detail::function_record>();
+                        /* Never append a method to an overload chain of a parent class;
+                           instead, hide the parent's overloads in this case */
+                        if (!chain->scope.is(rec->scope)) {
+                            chain = nullptr;
+                        }
+                    } else {
+                        chain = nullptr;
+                    }
                 }
             }
             // Don't trigger for things like the default __init__, which are wrapper_descriptors
@@ -495,6 +508,7 @@ protected:
             rec->def->ml_flags = METH_VARARGS | METH_KEYWORDS;
 
             capsule rec_capsule(unique_rec.release(),
+                                detail::get_function_record_capsule_name(),
                                 [](void *ptr) { destruct((detail::function_record *) ptr); });
             guarded_strdup.release();
 
@@ -661,10 +675,13 @@ protected:
     /// Main dispatch logic for calls to functions bound using pybind11
     static PyObject *dispatcher(PyObject *self, PyObject *args_in, PyObject *kwargs_in) {
         using namespace detail;
+        assert(isinstance<capsule>(self));
 
         /* Iterator over the list of potentially admissible overloads */
-        const function_record *overloads = (function_record *) PyCapsule_GetPointer(self, nullptr),
+        const function_record *overloads = reinterpret_cast<function_record *>(
+                                  PyCapsule_GetPointer(self, get_function_record_capsule_name())),
                               *it = overloads;
+        assert(overloads != nullptr);
 
         /* Need to know how many arguments + keyword arguments there are to pick the right
            overload */
@@ -1416,9 +1433,9 @@ template <typename T, enable_if_t<has_operator_delete<T>::value, int> = 0>
 void call_operator_delete(T *p, size_t, size_t) {
     T::operator delete(p);
 }
-template <
-    typename T,
-    enable_if_t<!has_operator_delete<T>::value && has_operator_delete_size<T>::value, int> = 0>
+template <typename T,
+          enable_if_t<!has_operator_delete<T>::value && has_operator_delete_size<T>::value, int>
+          = 0>
 void call_operator_delete(T *p, size_t s, size_t) {
     T::operator delete(p, s);
 }
@@ -1578,14 +1595,14 @@ public:
         return *this;
     }
 
-    template <detail::op_id id, detail::op_type ot, typename L, typename R, typename... Extra>
-    class_ &def(const detail::op_<id, ot, L, R> &op, const Extra &...extra) {
+    template <typename T, typename... Extra, detail::enable_if_t<T::op_enable_if_hook, int> = 0>
+    class_ &def(const T &op, const Extra &...extra) {
         op.execute(*this, extra...);
         return *this;
     }
 
-    template <detail::op_id id, detail::op_type ot, typename L, typename R, typename... Extra>
-    class_ &def_cast(const detail::op_<id, ot, L, R> &op, const Extra &...extra) {
+    template <typename T, typename... Extra, detail::enable_if_t<T::op_enable_if_hook, int> = 0>
+    class_ &def_cast(const T &op, const Extra &...extra) {
         op.execute_cast(*this, extra...);
         return *this;
     }
@@ -1719,7 +1736,8 @@ public:
     template <typename Getter, typename Setter, typename... Extra>
     class_ &
     def_property(const char *name, const Getter &fget, const Setter &fset, const Extra &...extra) {
-        return def_property(name, fget, cpp_function(method_adaptor<type>(fset)), extra...);
+        return def_property(
+            name, fget, cpp_function(method_adaptor<type>(fset), is_setter()), extra...);
     }
     template <typename Getter, typename... Extra>
     class_ &def_property(const char *name,
@@ -1830,8 +1848,7 @@ private:
         if (holder_ptr) {
             init_holder_from_existing(v_h, holder_ptr, std::is_copy_constructible<holder_type>());
             v_h.set_holder_constructed();
-        } else if (PYBIND11_SILENCE_MSVC_C4127(detail::always_construct_holder<holder_type>::value)
-                   || inst->owned) {
+        } else if (detail::always_construct_holder<holder_type>::value || inst->owned) {
             new (std::addressof(v_h.holder<holder_type>())) holder_type(v_h.value_ptr<type>());
             v_h.set_holder_constructed();
         }
@@ -1871,9 +1888,22 @@ private:
 
     static detail::function_record *get_function_record(handle h) {
         h = detail::get_function(h);
-        return h ? (detail::function_record *) reinterpret_borrow<capsule>(
-                   PyCFunction_GET_SELF(h.ptr()))
-                 : nullptr;
+        if (!h) {
+            return nullptr;
+        }
+
+        handle func_self = PyCFunction_GET_SELF(h.ptr());
+        if (!func_self) {
+            throw error_already_set();
+        }
+        if (!isinstance<capsule>(func_self)) {
+            return nullptr;
+        }
+        auto cap = reinterpret_borrow<capsule>(func_self);
+        if (!detail::is_function_record_capsule(cap)) {
+            return nullptr;
+        }
+        return cap.get_pointer<detail::function_record>();
     }
 };
 
@@ -1950,29 +1980,35 @@ struct enum_base {
             name("name"),
             is_method(m_base));
 
-        m_base.attr("__doc__") = static_property(
-            cpp_function(
-                [](handle arg) -> std::string {
-                    std::string docstring;
-                    dict entries = arg.attr("__entries");
-                    if (((PyTypeObject *) arg.ptr())->tp_doc) {
-                        docstring += std::string(((PyTypeObject *) arg.ptr())->tp_doc) + "\n\n";
-                    }
-                    docstring += "Members:";
-                    for (auto kv : entries) {
-                        auto key = std::string(pybind11::str(kv.first));
-                        auto comment = kv.second[int_(1)];
-                        docstring += "\n\n  " + key;
-                        if (!comment.is_none()) {
-                            docstring += " : " + (std::string) pybind11::str(comment);
+        if (options::show_enum_members_docstring()) {
+            m_base.attr("__doc__") = static_property(
+                cpp_function(
+                    [](handle arg) -> std::string {
+                        std::string docstring;
+                        dict entries = arg.attr("__entries");
+                        if (((PyTypeObject *) arg.ptr())->tp_doc) {
+                            docstring += std::string(
+                                reinterpret_cast<PyTypeObject *>(arg.ptr())->tp_doc);
+                            docstring += "\n\n";
                         }
-                    }
-                    return docstring;
-                },
-                name("__doc__")),
-            none(),
-            none(),
-            "");
+                        docstring += "Members:";
+                        for (auto kv : entries) {
+                            auto key = std::string(pybind11::str(kv.first));
+                            auto comment = kv.second[int_(1)];
+                            docstring += "\n\n  ";
+                            docstring += key;
+                            if (!comment.is_none()) {
+                                docstring += " : ";
+                                docstring += pybind11::str(comment).cast<std::string>();
+                            }
+                        }
+                        return docstring;
+                    },
+                    name("__doc__")),
+                none(),
+                none(),
+                "");
+        }
 
         m_base.attr("__members__") = static_property(cpp_function(
                                                          [](handle arg) -> dict {
@@ -2073,7 +2109,7 @@ struct enum_base {
                               + "\" already exists!");
         }
 
-        entries[name] = std::make_pair(value, doc);
+        entries[name] = pybind11::make_tuple(value, doc);
         m_base.attr(std::move(name)) = std::move(value);
     }
 
@@ -2333,7 +2369,7 @@ template <typename Access,
           typename Sentinel,
           typename ValueType,
           typename... Extra>
-iterator make_iterator_impl(Iterator &&first, Sentinel &&last, Extra &&...extra) {
+iterator make_iterator_impl(Iterator first, Sentinel last, Extra &&...extra) {
     using state = detail::iterator_state<Access, Policy, Iterator, Sentinel, ValueType, Extra...>;
     // TODO: state captures only the types of Extra, not the values
 
@@ -2359,7 +2395,7 @@ iterator make_iterator_impl(Iterator &&first, Sentinel &&last, Extra &&...extra)
                 Policy);
     }
 
-    return cast(state{std::forward<Iterator>(first), std::forward<Sentinel>(last), true});
+    return cast(state{first, last, true});
 }
 
 PYBIND11_NAMESPACE_END(detail)
@@ -2370,15 +2406,13 @@ template <return_value_policy Policy = return_value_policy::reference_internal,
           typename Sentinel,
           typename ValueType = typename detail::iterator_access<Iterator>::result_type,
           typename... Extra>
-iterator make_iterator(Iterator &&first, Sentinel &&last, Extra &&...extra) {
+iterator make_iterator(Iterator first, Sentinel last, Extra &&...extra) {
     return detail::make_iterator_impl<detail::iterator_access<Iterator>,
                                       Policy,
                                       Iterator,
                                       Sentinel,
                                       ValueType,
-                                      Extra...>(std::forward<Iterator>(first),
-                                                std::forward<Sentinel>(last),
-                                                std::forward<Extra>(extra)...);
+                                      Extra...>(first, last, std::forward<Extra>(extra)...);
 }
 
 /// Makes a python iterator over the keys (`.first`) of a iterator over pairs from a
@@ -2388,15 +2422,13 @@ template <return_value_policy Policy = return_value_policy::reference_internal,
           typename Sentinel,
           typename KeyType = typename detail::iterator_key_access<Iterator>::result_type,
           typename... Extra>
-iterator make_key_iterator(Iterator &&first, Sentinel &&last, Extra &&...extra) {
+iterator make_key_iterator(Iterator first, Sentinel last, Extra &&...extra) {
     return detail::make_iterator_impl<detail::iterator_key_access<Iterator>,
                                       Policy,
                                       Iterator,
                                       Sentinel,
                                       KeyType,
-                                      Extra...>(std::forward<Iterator>(first),
-                                                std::forward<Sentinel>(last),
-                                                std::forward<Extra>(extra)...);
+                                      Extra...>(first, last, std::forward<Extra>(extra)...);
 }
 
 /// Makes a python iterator over the values (`.second`) of a iterator over pairs from a
@@ -2406,15 +2438,13 @@ template <return_value_policy Policy = return_value_policy::reference_internal,
           typename Sentinel,
           typename ValueType = typename detail::iterator_value_access<Iterator>::result_type,
           typename... Extra>
-iterator make_value_iterator(Iterator &&first, Sentinel &&last, Extra &&...extra) {
+iterator make_value_iterator(Iterator first, Sentinel last, Extra &&...extra) {
     return detail::make_iterator_impl<detail::iterator_value_access<Iterator>,
                                       Policy,
                                       Iterator,
                                       Sentinel,
                                       ValueType,
-                                      Extra...>(std::forward<Iterator>(first),
-                                                std::forward<Sentinel>(last),
-                                                std::forward<Extra>(extra)...);
+                                      Extra...>(first, last, std::forward<Extra>(extra)...);
 }
 
 /// Makes an iterator over values of an stl container or other container supporting
@@ -2858,7 +2888,3 @@ inline function get_overload(const T *this_ptr, const char *name) {
     PYBIND11_OVERRIDE_PURE(PYBIND11_TYPE(ret_type), PYBIND11_TYPE(cname), fn, __VA_ARGS__);
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-
-#if defined(__GNUC__) && __GNUC__ == 7
-#    pragma GCC diagnostic pop // -Wnoexcept-type
-#endif
diff --git a/wrap/pybind11/include/pybind11/pytypes.h b/wrap/pybind11/include/pybind11/pytypes.h
index 339b0961e..64aad6347 100644
--- a/wrap/pybind11/include/pybind11/pytypes.h
+++ b/wrap/pybind11/include/pybind11/pytypes.h
@@ -33,6 +33,8 @@
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
 /* A few forward declarations */
 class handle;
 class object;
@@ -155,23 +157,23 @@ public:
     object operator-() const;
     object operator~() const;
     object operator+(object_api const &other) const;
-    object operator+=(object_api const &other) const;
+    object operator+=(object_api const &other);
     object operator-(object_api const &other) const;
-    object operator-=(object_api const &other) const;
+    object operator-=(object_api const &other);
     object operator*(object_api const &other) const;
-    object operator*=(object_api const &other) const;
+    object operator*=(object_api const &other);
     object operator/(object_api const &other) const;
-    object operator/=(object_api const &other) const;
+    object operator/=(object_api const &other);
     object operator|(object_api const &other) const;
-    object operator|=(object_api const &other) const;
+    object operator|=(object_api const &other);
     object operator&(object_api const &other) const;
-    object operator&=(object_api const &other) const;
+    object operator&=(object_api const &other);
     object operator^(object_api const &other) const;
-    object operator^=(object_api const &other) const;
+    object operator^=(object_api const &other);
     object operator<<(object_api const &other) const;
-    object operator<<=(object_api const &other) const;
+    object operator<<=(object_api const &other);
     object operator>>(object_api const &other) const;
-    object operator>>=(object_api const &other) const;
+    object operator>>=(object_api const &other);
 
     PYBIND11_DEPRECATED("Use py::str(obj) instead")
     pybind11::str str() const;
@@ -230,7 +232,8 @@ public:
         detail::enable_if_t<detail::all_of<detail::none_of<std::is_base_of<handle, T>,
                                                            detail::is_pyobj_ptr_or_nullptr_t<T>>,
                                            std::is_convertible<T, PyObject *>>::value,
-                            int> = 0>
+                            int>
+        = 0>
     // NOLINTNEXTLINE(google-explicit-constructor)
     handle(T &obj) : m_ptr(obj) {}
 
@@ -246,6 +249,11 @@ public:
     const handle &inc_ref() const & {
 #ifdef PYBIND11_HANDLE_REF_DEBUG
         inc_ref_counter(1);
+#endif
+#ifdef PYBIND11_ASSERT_GIL_HELD_INCREF_DECREF
+        if (m_ptr != nullptr && !PyGILState_Check()) {
+            throw_gilstate_error("pybind11::handle::inc_ref()");
+        }
 #endif
         Py_XINCREF(m_ptr);
         return *this;
@@ -257,6 +265,11 @@ public:
         this function automatically. Returns a reference to itself.
     \endrst */
     const handle &dec_ref() const & {
+#ifdef PYBIND11_ASSERT_GIL_HELD_INCREF_DECREF
+        if (m_ptr != nullptr && !PyGILState_Check()) {
+            throw_gilstate_error("pybind11::handle::dec_ref()");
+        }
+#endif
         Py_XDECREF(m_ptr);
         return *this;
     }
@@ -283,8 +296,33 @@ public:
 protected:
     PyObject *m_ptr = nullptr;
 
-#ifdef PYBIND11_HANDLE_REF_DEBUG
 private:
+#ifdef PYBIND11_ASSERT_GIL_HELD_INCREF_DECREF
+    void throw_gilstate_error(const std::string &function_name) const {
+        fprintf(
+            stderr,
+            "%s is being called while the GIL is either not held or invalid. Please see "
+            "https://pybind11.readthedocs.io/en/stable/advanced/"
+            "misc.html#common-sources-of-global-interpreter-lock-errors for debugging advice.\n"
+            "If you are convinced there is no bug in your code, you can #define "
+            "PYBIND11_NO_ASSERT_GIL_HELD_INCREF_DECREF"
+            "to disable this check. In that case you have to ensure this #define is consistently "
+            "used for all translation units linked into a given pybind11 extension, otherwise "
+            "there will be ODR violations.",
+            function_name.c_str());
+        fflush(stderr);
+        if (Py_TYPE(m_ptr)->tp_name != nullptr) {
+            fprintf(stderr,
+                    "The failing %s call was triggered on a %s object.\n",
+                    function_name.c_str(),
+                    Py_TYPE(m_ptr)->tp_name);
+            fflush(stderr);
+        }
+        throw std::runtime_error(function_name + " PyGILState_Check() failure.");
+    }
+#endif
+
+#ifdef PYBIND11_HANDLE_REF_DEBUG
     static std::size_t inc_ref_counter(std::size_t add) {
         thread_local std::size_t counter = 0;
         counter += add;
@@ -334,12 +372,15 @@ public:
     }
 
     object &operator=(const object &other) {
-        other.inc_ref();
-        // Use temporary variable to ensure `*this` remains valid while
-        // `Py_XDECREF` executes, in case `*this` is accessible from Python.
-        handle temp(m_ptr);
-        m_ptr = other.m_ptr;
-        temp.dec_ref();
+        // Skip inc_ref and dec_ref if both objects are the same
+        if (!this->is(other)) {
+            other.inc_ref();
+            // Use temporary variable to ensure `*this` remains valid while
+            // `Py_XDECREF` executes, in case `*this` is accessible from Python.
+            handle temp(m_ptr);
+            m_ptr = other.m_ptr;
+            temp.dec_ref();
+        }
         return *this;
     }
 
@@ -353,6 +394,20 @@ public:
         return *this;
     }
 
+#define PYBIND11_INPLACE_OP(iop)                                                                  \
+    object iop(object_api const &other) { return operator=(handle::iop(other)); }
+
+    PYBIND11_INPLACE_OP(operator+=)
+    PYBIND11_INPLACE_OP(operator-=)
+    PYBIND11_INPLACE_OP(operator*=)
+    PYBIND11_INPLACE_OP(operator/=)
+    PYBIND11_INPLACE_OP(operator|=)
+    PYBIND11_INPLACE_OP(operator&=)
+    PYBIND11_INPLACE_OP(operator^=)
+    PYBIND11_INPLACE_OP(operator<<=)
+    PYBIND11_INPLACE_OP(operator>>=)
+#undef PYBIND11_INPLACE_OP
+
     // Calling cast() on an object lvalue just copies (via handle::cast)
     template <typename T>
     T cast() const &;
@@ -413,7 +468,7 @@ PYBIND11_NAMESPACE_BEGIN(detail)
 
 // Equivalent to obj.__class__.__name__ (or obj.__name__ if obj is a class).
 inline const char *obj_class_name(PyObject *obj) {
-    if (Py_TYPE(obj) == &PyType_Type) {
+    if (PyType_Check(obj)) {
         return reinterpret_cast<PyTypeObject *>(obj)->tp_name;
     }
     return Py_TYPE(obj)->tp_name;
@@ -421,13 +476,24 @@ inline const char *obj_class_name(PyObject *obj) {
 
 std::string error_string();
 
+// The code in this struct is very unusual, to minimize the chances of
+// masking bugs (elsewhere) by errors during the error handling (here).
+// This is meant to be a lifeline for troubleshooting long-running processes
+// that crash under conditions that are virtually impossible to reproduce.
+// Low-level implementation alternatives are preferred to higher-level ones
+// that might raise cascading exceptions. Last-ditch-kind-of attempts are made
+// to report as much of the original error as possible, even if there are
+// secondary issues obtaining some of the details.
 struct error_fetch_and_normalize {
-    // Immediate normalization is long-established behavior (starting with
-    // https://github.com/pybind/pybind11/commit/135ba8deafb8bf64a15b24d1513899eb600e2011
-    // from Sep 2016) and safest. Normalization could be deferred, but this could mask
-    // errors elsewhere, the performance gain is very minor in typical situations
-    // (usually the dominant bottleneck is EH unwinding), and the implementation here
-    // would be more complex.
+    // This comment only applies to Python <= 3.11:
+    //     Immediate normalization is long-established behavior (starting with
+    //     https://github.com/pybind/pybind11/commit/135ba8deafb8bf64a15b24d1513899eb600e2011
+    //     from Sep 2016) and safest. Normalization could be deferred, but this could mask
+    //     errors elsewhere, the performance gain is very minor in typical situations
+    //     (usually the dominant bottleneck is EH unwinding), and the implementation here
+    //     would be more complex.
+    // Starting with Python 3.12, PyErr_Fetch() normalizes exceptions immediately.
+    // Any errors during normalization are tracked under __notes__.
     explicit error_fetch_and_normalize(const char *called) {
         PyErr_Fetch(&m_type.ptr(), &m_value.ptr(), &m_trace.ptr());
         if (!m_type) {
@@ -442,6 +508,14 @@ struct error_fetch_and_normalize {
                             "of the original active exception type.");
         }
         m_lazy_error_string = exc_type_name_orig;
+#if PY_VERSION_HEX >= 0x030C0000
+        // The presence of __notes__ is likely due to exception normalization
+        // errors, although that is not necessarily true, therefore insert a
+        // hint only:
+        if (PyObject_HasAttrString(m_value.ptr(), "__notes__")) {
+            m_lazy_error_string += "[WITH __notes__]";
+        }
+#else
         // PyErr_NormalizeException() may change the exception type if there are cascading
         // failures. This can potentially be extremely confusing.
         PyErr_NormalizeException(&m_type.ptr(), &m_value.ptr(), &m_trace.ptr());
@@ -451,11 +525,17 @@ struct error_fetch_and_normalize {
                             "active exception.");
         }
         const char *exc_type_name_norm = detail::obj_class_name(m_type.ptr());
-        if (exc_type_name_orig == nullptr) {
+        if (exc_type_name_norm == nullptr) {
             pybind11_fail("Internal error: " + std::string(called)
                           + " failed to obtain the name "
                             "of the normalized active exception type.");
         }
+#    if defined(PYPY_VERSION_NUM) && PYPY_VERSION_NUM < 0x07030a00
+        // This behavior runs the risk of masking errors in the error handling, but avoids a
+        // conflict with PyPy, which relies on the normalization here to change OSError to
+        // FileNotFoundError (https://github.com/pybind/pybind11/issues/4075).
+        m_lazy_error_string = exc_type_name_norm;
+#    else
         if (exc_type_name_norm != m_lazy_error_string) {
             std::string msg = std::string(called)
                               + ": MISMATCH of original and normalized "
@@ -467,6 +547,8 @@ struct error_fetch_and_normalize {
             msg += ": " + format_value_and_trace();
             pybind11_fail(msg);
         }
+#    endif
+#endif
     }
 
     error_fetch_and_normalize(const error_fetch_and_normalize &) = delete;
@@ -477,12 +559,64 @@ struct error_fetch_and_normalize {
         std::string message_error_string;
         if (m_value) {
             auto value_str = reinterpret_steal<object>(PyObject_Str(m_value.ptr()));
+            constexpr const char *message_unavailable_exc
+                = "<MESSAGE UNAVAILABLE DUE TO ANOTHER EXCEPTION>";
             if (!value_str) {
                 message_error_string = detail::error_string();
-                result = "<MESSAGE UNAVAILABLE DUE TO ANOTHER EXCEPTION>";
+                result = message_unavailable_exc;
             } else {
-                result = value_str.cast<std::string>();
+                // Not using `value_str.cast<std::string>()`, to not potentially throw a secondary
+                // error_already_set that will then result in process termination (#4288).
+                auto value_bytes = reinterpret_steal<object>(
+                    PyUnicode_AsEncodedString(value_str.ptr(), "utf-8", "backslashreplace"));
+                if (!value_bytes) {
+                    message_error_string = detail::error_string();
+                    result = message_unavailable_exc;
+                } else {
+                    char *buffer = nullptr;
+                    Py_ssize_t length = 0;
+                    if (PyBytes_AsStringAndSize(value_bytes.ptr(), &buffer, &length) == -1) {
+                        message_error_string = detail::error_string();
+                        result = message_unavailable_exc;
+                    } else {
+                        result = std::string(buffer, static_cast<std::size_t>(length));
+                    }
+                }
             }
+#if PY_VERSION_HEX >= 0x030B0000
+            auto notes
+                = reinterpret_steal<object>(PyObject_GetAttrString(m_value.ptr(), "__notes__"));
+            if (!notes) {
+                PyErr_Clear(); // No notes is good news.
+            } else {
+                auto len_notes = PyList_Size(notes.ptr());
+                if (len_notes < 0) {
+                    result += "\nFAILURE obtaining len(__notes__): " + detail::error_string();
+                } else {
+                    result += "\n__notes__ (len=" + std::to_string(len_notes) + "):";
+                    for (ssize_t i = 0; i < len_notes; i++) {
+                        PyObject *note = PyList_GET_ITEM(notes.ptr(), i);
+                        auto note_bytes = reinterpret_steal<object>(
+                            PyUnicode_AsEncodedString(note, "utf-8", "backslashreplace"));
+                        if (!note_bytes) {
+                            result += "\nFAILURE obtaining __notes__[" + std::to_string(i)
+                                      + "]: " + detail::error_string();
+                        } else {
+                            char *buffer = nullptr;
+                            Py_ssize_t length = 0;
+                            if (PyBytes_AsStringAndSize(note_bytes.ptr(), &buffer, &length)
+                                == -1) {
+                                result += "\nFAILURE formatting __notes__[" + std::to_string(i)
+                                          + "]: " + detail::error_string();
+                            } else {
+                                result += '\n';
+                                result += std::string(buffer, static_cast<std::size_t>(length));
+                            }
+                        }
+                    }
+                }
+            }
+#endif
         } else {
             result = "<MESSAGE UNAVAILABLE>";
         }
@@ -581,12 +715,6 @@ inline std::string error_string() {
 
 PYBIND11_NAMESPACE_END(detail)
 
-#if defined(_MSC_VER)
-#    pragma warning(push)
-#    pragma warning(disable : 4275 4251)
-//     warning C4275: An exported class was derived from a class that wasn't exported.
-//     Can be ignored when derived from a STL class.
-#endif
 /// Fetch and hold an error which was already set in Python.  An instance of this is typically
 /// thrown to propagate python-side errors back through C++ which can either be caught manually or
 /// else falls back to the function dispatcher (which then raises the captured error back to
@@ -646,9 +774,6 @@ private:
     ///          crashes (undefined behavior) if the Python interpreter is finalizing.
     static void m_fetched_error_deleter(detail::error_fetch_and_normalize *raw_ptr);
 };
-#if defined(_MSC_VER)
-#    pragma warning(pop)
-#endif
 
 /// Replaces the current Python error indicator with the chosen error, performing a
 /// 'raise from' to indicate that the chosen error was caused by the original error.
@@ -851,10 +976,8 @@ object object_or_cast(T &&o);
 // Match a PyObject*, which we want to convert directly to handle via its converting constructor
 inline handle object_or_cast(PyObject *ptr) { return ptr; }
 
-#if defined(_MSC_VER) && _MSC_VER < 1920
-#    pragma warning(push)
-#    pragma warning(disable : 4522) // warning C4522: multiple assignment operators specified
-#endif
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_MSVC(4522) // warning C4522: multiple assignment operators specified
 template <typename Policy>
 class accessor : public object_api<accessor<Policy>> {
     using key_type = typename Policy::key_type;
@@ -918,9 +1041,7 @@ private:
     key_type key;
     mutable object cache;
 };
-#if defined(_MSC_VER) && _MSC_VER < 1920
-#    pragma warning(pop)
-#endif
+PYBIND11_WARNING_POP
 
 PYBIND11_NAMESPACE_BEGIN(accessor_policies)
 struct obj_attr {
@@ -1266,7 +1387,7 @@ public:
 
 #define PYBIND11_OBJECT_CVT_DEFAULT(Name, Parent, CheckFun, ConvertFun)                           \
     PYBIND11_OBJECT_CVT(Name, Parent, CheckFun, ConvertFun)                                       \
-    Name() : Parent() {}
+    Name() = default;
 
 #define PYBIND11_OBJECT_CHECK_FAILED(Name, o_ptr)                                                 \
     ::pybind11::type_error("Object of type '"                                                     \
@@ -1289,7 +1410,7 @@ public:
 
 #define PYBIND11_OBJECT_DEFAULT(Name, Parent, CheckFun)                                           \
     PYBIND11_OBJECT(Name, Parent, CheckFun)                                                       \
-    Name() : Parent() {}
+    Name() = default;
 
 /// \addtogroup pytypes
 /// @{
@@ -1358,7 +1479,7 @@ public:
 private:
     void advance() {
         value = reinterpret_steal<object>(PyIter_Next(m_ptr));
-        if (PyErr_Occurred()) {
+        if (value.ptr() == nullptr && PyErr_Occurred()) {
             throw error_already_set();
         }
     }
@@ -1408,6 +1529,9 @@ public:
     str(const char *c, const SzType &n)
         : object(PyUnicode_FromStringAndSize(c, ssize_t_cast(n)), stolen_t{}) {
         if (!m_ptr) {
+            if (PyErr_Occurred()) {
+                throw error_already_set();
+            }
             pybind11_fail("Could not allocate string object!");
         }
     }
@@ -1417,6 +1541,9 @@ public:
     // NOLINTNEXTLINE(google-explicit-constructor)
     str(const char *c = "") : object(PyUnicode_FromString(c), stolen_t{}) {
         if (!m_ptr) {
+            if (PyErr_Occurred()) {
+                throw error_already_set();
+            }
             pybind11_fail("Could not allocate string object!");
         }
     }
@@ -1574,6 +1701,9 @@ inline str::str(const bytes &b) {
     }
     auto obj = reinterpret_steal<object>(PyUnicode_FromStringAndSize(buffer, length));
     if (!obj) {
+        if (PyErr_Occurred()) {
+            throw error_already_set();
+        }
         pybind11_fail("Could not allocate string object!");
     }
     m_ptr = obj.release().ptr();
@@ -1651,7 +1781,7 @@ PYBIND11_NAMESPACE_BEGIN(detail)
 // unsigned type: (A)-1 != (B)-1 when A and B are unsigned types of different sizes).
 template <typename Unsigned>
 Unsigned as_unsigned(PyObject *o) {
-    if (PYBIND11_SILENCE_MSVC_C4127(sizeof(Unsigned) <= sizeof(unsigned long))) {
+    if (sizeof(Unsigned) <= sizeof(unsigned long)) {
         unsigned long v = PyLong_AsUnsignedLong(o);
         return v == (unsigned long) -1 && PyErr_Occurred() ? (Unsigned) -1 : (Unsigned) v;
     }
@@ -1668,7 +1798,7 @@ public:
     template <typename T, detail::enable_if_t<std::is_integral<T>::value, int> = 0>
     // NOLINTNEXTLINE(google-explicit-constructor)
     int_(T value) {
-        if (PYBIND11_SILENCE_MSVC_C4127(sizeof(T) <= sizeof(long))) {
+        if (sizeof(T) <= sizeof(long)) {
             if (std::is_signed<T>::value) {
                 m_ptr = PyLong_FromLong((long) value);
             } else {
@@ -1785,43 +1915,28 @@ public:
 
     explicit capsule(const void *value,
                      const char *name = nullptr,
-                     void (*destructor)(PyObject *) = nullptr)
+                     PyCapsule_Destructor destructor = nullptr)
         : object(PyCapsule_New(const_cast<void *>(value), name, destructor), stolen_t{}) {
         if (!m_ptr) {
             throw error_already_set();
         }
     }
 
-    PYBIND11_DEPRECATED("Please pass a destructor that takes a void pointer as input")
-    capsule(const void *value, void (*destruct)(PyObject *))
-        : object(PyCapsule_New(const_cast<void *>(value), nullptr, destruct), stolen_t{}) {
+    PYBIND11_DEPRECATED("Please use the ctor with value, name, destructor args")
+    capsule(const void *value, PyCapsule_Destructor destructor)
+        : object(PyCapsule_New(const_cast<void *>(value), nullptr, destructor), stolen_t{}) {
         if (!m_ptr) {
             throw error_already_set();
         }
     }
 
+    /// Capsule name is nullptr.
     capsule(const void *value, void (*destructor)(void *)) {
-        m_ptr = PyCapsule_New(const_cast<void *>(value), nullptr, [](PyObject *o) {
-            // guard if destructor called while err indicator is set
-            error_scope error_guard;
-            auto destructor = reinterpret_cast<void (*)(void *)>(PyCapsule_GetContext(o));
-            if (destructor == nullptr) {
-                if (PyErr_Occurred()) {
-                    throw error_already_set();
-                }
-                pybind11_fail("Unable to get capsule context");
-            }
-            const char *name = get_name_in_error_scope(o);
-            void *ptr = PyCapsule_GetPointer(o, name);
-            if (ptr == nullptr) {
-                throw error_already_set();
-            }
-            destructor(ptr);
-        });
+        initialize_with_void_ptr_destructor(value, nullptr, destructor);
+    }
 
-        if (!m_ptr || PyCapsule_SetContext(m_ptr, (void *) destructor) != 0) {
-            throw error_already_set();
-        }
+    capsule(const void *value, const char *name, void (*destructor)(void *)) {
+        initialize_with_void_ptr_destructor(value, name, destructor);
     }
 
     explicit capsule(void (*destructor)()) {
@@ -1889,6 +2004,32 @@ private:
 
         return name;
     }
+
+    void initialize_with_void_ptr_destructor(const void *value,
+                                             const char *name,
+                                             void (*destructor)(void *)) {
+        m_ptr = PyCapsule_New(const_cast<void *>(value), name, [](PyObject *o) {
+            // guard if destructor called while err indicator is set
+            error_scope error_guard;
+            auto destructor = reinterpret_cast<void (*)(void *)>(PyCapsule_GetContext(o));
+            if (destructor == nullptr && PyErr_Occurred()) {
+                throw error_already_set();
+            }
+            const char *name = get_name_in_error_scope(o);
+            void *ptr = PyCapsule_GetPointer(o, name);
+            if (ptr == nullptr) {
+                throw error_already_set();
+            }
+
+            if (destructor != nullptr) {
+                destructor(ptr);
+            }
+        });
+
+        if (!m_ptr || PyCapsule_SetContext(m_ptr, reinterpret_cast<void *>(destructor)) != 0) {
+            throw error_already_set();
+        }
+    }
 };
 
 class tuple : public object {
@@ -1943,7 +2084,11 @@ public:
     void clear() /* py-non-const */ { PyDict_Clear(ptr()); }
     template <typename T>
     bool contains(T &&key) const {
-        return PyDict_Contains(m_ptr, detail::object_or_cast(std::forward<T>(key)).ptr()) == 1;
+        auto result = PyDict_Contains(m_ptr, detail::object_or_cast(std::forward<T>(key)).ptr());
+        if (result == -1) {
+            throw error_already_set();
+        }
+        return result == 1;
     }
 
 private:
@@ -1998,14 +2143,20 @@ public:
     detail::list_iterator end() const { return {*this, PyList_GET_SIZE(m_ptr)}; }
     template <typename T>
     void append(T &&val) /* py-non-const */ {
-        PyList_Append(m_ptr, detail::object_or_cast(std::forward<T>(val)).ptr());
+        if (PyList_Append(m_ptr, detail::object_or_cast(std::forward<T>(val)).ptr()) != 0) {
+            throw error_already_set();
+        }
     }
     template <typename IdxType,
               typename ValType,
               detail::enable_if_t<std::is_integral<IdxType>::value, int> = 0>
     void insert(const IdxType &index, ValType &&val) /* py-non-const */ {
-        PyList_Insert(
-            m_ptr, ssize_t_cast(index), detail::object_or_cast(std::forward<ValType>(val)).ptr());
+        if (PyList_Insert(m_ptr,
+                          ssize_t_cast(index),
+                          detail::object_or_cast(std::forward<ValType>(val)).ptr())
+            != 0) {
+            throw error_already_set();
+        }
     }
 };
 
@@ -2023,7 +2174,11 @@ public:
     bool empty() const { return size() == 0; }
     template <typename T>
     bool contains(T &&val) const {
-        return PySet_Contains(m_ptr, detail::object_or_cast(std::forward<T>(val)).ptr()) == 1;
+        auto result = PySet_Contains(m_ptr, detail::object_or_cast(std::forward<T>(val)).ptr());
+        if (result == -1) {
+            throw error_already_set();
+        }
+        return result == 1;
     }
 };
 
@@ -2364,29 +2519,39 @@ bool object_api<D>::rich_compare(object_api const &other, int value) const {
         return result;                                                                            \
     }
 
+#define PYBIND11_MATH_OPERATOR_BINARY_INPLACE(iop, fn)                                            \
+    template <typename D>                                                                         \
+    object object_api<D>::iop(object_api const &other) {                                          \
+        object result = reinterpret_steal<object>(fn(derived().ptr(), other.derived().ptr()));    \
+        if (!result.ptr())                                                                        \
+            throw error_already_set();                                                            \
+        return result;                                                                            \
+    }
+
 PYBIND11_MATH_OPERATOR_UNARY(operator~, PyNumber_Invert)
 PYBIND11_MATH_OPERATOR_UNARY(operator-, PyNumber_Negative)
 PYBIND11_MATH_OPERATOR_BINARY(operator+, PyNumber_Add)
-PYBIND11_MATH_OPERATOR_BINARY(operator+=, PyNumber_InPlaceAdd)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator+=, PyNumber_InPlaceAdd)
 PYBIND11_MATH_OPERATOR_BINARY(operator-, PyNumber_Subtract)
-PYBIND11_MATH_OPERATOR_BINARY(operator-=, PyNumber_InPlaceSubtract)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator-=, PyNumber_InPlaceSubtract)
 PYBIND11_MATH_OPERATOR_BINARY(operator*, PyNumber_Multiply)
-PYBIND11_MATH_OPERATOR_BINARY(operator*=, PyNumber_InPlaceMultiply)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator*=, PyNumber_InPlaceMultiply)
 PYBIND11_MATH_OPERATOR_BINARY(operator/, PyNumber_TrueDivide)
-PYBIND11_MATH_OPERATOR_BINARY(operator/=, PyNumber_InPlaceTrueDivide)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator/=, PyNumber_InPlaceTrueDivide)
 PYBIND11_MATH_OPERATOR_BINARY(operator|, PyNumber_Or)
-PYBIND11_MATH_OPERATOR_BINARY(operator|=, PyNumber_InPlaceOr)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator|=, PyNumber_InPlaceOr)
 PYBIND11_MATH_OPERATOR_BINARY(operator&, PyNumber_And)
-PYBIND11_MATH_OPERATOR_BINARY(operator&=, PyNumber_InPlaceAnd)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator&=, PyNumber_InPlaceAnd)
 PYBIND11_MATH_OPERATOR_BINARY(operator^, PyNumber_Xor)
-PYBIND11_MATH_OPERATOR_BINARY(operator^=, PyNumber_InPlaceXor)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator^=, PyNumber_InPlaceXor)
 PYBIND11_MATH_OPERATOR_BINARY(operator<<, PyNumber_Lshift)
-PYBIND11_MATH_OPERATOR_BINARY(operator<<=, PyNumber_InPlaceLshift)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator<<=, PyNumber_InPlaceLshift)
 PYBIND11_MATH_OPERATOR_BINARY(operator>>, PyNumber_Rshift)
-PYBIND11_MATH_OPERATOR_BINARY(operator>>=, PyNumber_InPlaceRshift)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator>>=, PyNumber_InPlaceRshift)
 
 #undef PYBIND11_MATH_OPERATOR_UNARY
 #undef PYBIND11_MATH_OPERATOR_BINARY
+#undef PYBIND11_MATH_OPERATOR_BINARY_INPLACE
 
 PYBIND11_NAMESPACE_END(detail)
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
diff --git a/wrap/pybind11/include/pybind11/stl.h b/wrap/pybind11/include/pybind11/stl.h
index ab30ecac0..f39f44f7c 100644
--- a/wrap/pybind11/include/pybind11/stl.h
+++ b/wrap/pybind11/include/pybind11/stl.h
@@ -45,21 +45,35 @@ using forwarded_type = conditional_t<std::is_lvalue_reference<T>::value,
 /// Forwards a value U as rvalue or lvalue according to whether T is rvalue or lvalue; typically
 /// used for forwarding a container's elements.
 template <typename T, typename U>
-forwarded_type<T, U> forward_like(U &&u) {
+constexpr forwarded_type<T, U> forward_like(U &&u) {
     return std::forward<detail::forwarded_type<T, U>>(std::forward<U>(u));
 }
 
+// Checks if a container has a STL style reserve method.
+// This will only return true for a `reserve()` with a `void` return.
+template <typename C>
+using has_reserve_method = std::is_same<decltype(std::declval<C>().reserve(0)), void>;
+
 template <typename Type, typename Key>
 struct set_caster {
     using type = Type;
     using key_conv = make_caster<Key>;
 
+private:
+    template <typename T = Type, enable_if_t<has_reserve_method<T>::value, int> = 0>
+    void reserve_maybe(const anyset &s, Type *) {
+        value.reserve(s.size());
+    }
+    void reserve_maybe(const anyset &, void *) {}
+
+public:
     bool load(handle src, bool convert) {
         if (!isinstance<anyset>(src)) {
             return false;
         }
         auto s = reinterpret_borrow<anyset>(src);
         value.clear();
+        reserve_maybe(s, &value);
         for (auto entry : s) {
             key_conv conv;
             if (!conv.load(entry, convert)) {
@@ -78,7 +92,7 @@ struct set_caster {
         pybind11::set s;
         for (auto &&value : src) {
             auto value_ = reinterpret_steal<object>(
-                key_conv::cast(forward_like<T>(value), policy, parent));
+                key_conv::cast(detail::forward_like<T>(value), policy, parent));
             if (!value_ || !s.add(std::move(value_))) {
                 return handle();
             }
@@ -94,12 +108,21 @@ struct map_caster {
     using key_conv = make_caster<Key>;
     using value_conv = make_caster<Value>;
 
+private:
+    template <typename T = Type, enable_if_t<has_reserve_method<T>::value, int> = 0>
+    void reserve_maybe(const dict &d, Type *) {
+        value.reserve(d.size());
+    }
+    void reserve_maybe(const dict &, void *) {}
+
+public:
     bool load(handle src, bool convert) {
         if (!isinstance<dict>(src)) {
             return false;
         }
         auto d = reinterpret_borrow<dict>(src);
         value.clear();
+        reserve_maybe(d, &value);
         for (auto it : d) {
             key_conv kconv;
             value_conv vconv;
@@ -122,9 +145,9 @@ struct map_caster {
         }
         for (auto &&kv : src) {
             auto key = reinterpret_steal<object>(
-                key_conv::cast(forward_like<T>(kv.first), policy_key, parent));
+                key_conv::cast(detail::forward_like<T>(kv.first), policy_key, parent));
             auto value = reinterpret_steal<object>(
-                value_conv::cast(forward_like<T>(kv.second), policy_value, parent));
+                value_conv::cast(detail::forward_like<T>(kv.second), policy_value, parent));
             if (!key || !value) {
                 return handle();
             }
@@ -160,9 +183,7 @@ struct list_caster {
     }
 
 private:
-    template <
-        typename T = Type,
-        enable_if_t<std::is_same<decltype(std::declval<T>().reserve(0)), void>::value, int> = 0>
+    template <typename T = Type, enable_if_t<has_reserve_method<T>::value, int> = 0>
     void reserve_maybe(const sequence &s, Type *) {
         value.reserve(s.size());
     }
@@ -178,7 +199,7 @@ public:
         ssize_t index = 0;
         for (auto &&value : src) {
             auto value_ = reinterpret_steal<object>(
-                value_conv::cast(forward_like<T>(value), policy, parent));
+                value_conv::cast(detail::forward_like<T>(value), policy, parent));
             if (!value_) {
                 return handle();
             }
@@ -242,7 +263,7 @@ public:
         ssize_t index = 0;
         for (auto &&value : src) {
             auto value_ = reinterpret_steal<object>(
-                value_conv::cast(forward_like<T>(value), policy, parent));
+                value_conv::cast(detail::forward_like<T>(value), policy, parent));
             if (!value_) {
                 return handle();
             }
@@ -252,11 +273,11 @@ public:
     }
 
     PYBIND11_TYPE_CASTER(ArrayType,
-                         const_name("List[") + value_conv::name
+                         const_name<Resizable>(const_name(""), const_name("Annotated["))
+                             + const_name("List[") + value_conv::name + const_name("]")
                              + const_name<Resizable>(const_name(""),
-                                                     const_name("[") + const_name<Size>()
-                                                         + const_name("]"))
-                             + const_name("]"));
+                                                     const_name(", FixedSize(")
+                                                         + const_name<Size>() + const_name(")]")));
 };
 
 template <typename Type, size_t Size>
@@ -290,11 +311,12 @@ struct optional_caster {
     template <typename T>
     static handle cast(T &&src, return_value_policy policy, handle parent) {
         if (!src) {
-            return none().inc_ref();
+            return none().release();
         }
         if (!std::is_lvalue_reference<T>::value) {
             policy = return_value_policy_override<Value>::policy(policy);
         }
+        // NOLINTNEXTLINE(bugprone-unchecked-optional-access)
         return value_conv::cast(*std::forward<T>(src), policy, parent);
     }
 
diff --git a/wrap/pybind11/include/pybind11/stl_bind.h b/wrap/pybind11/include/pybind11/stl_bind.h
index 22a29b476..49f1b7782 100644
--- a/wrap/pybind11/include/pybind11/stl_bind.h
+++ b/wrap/pybind11/include/pybind11/stl_bind.h
@@ -10,10 +10,13 @@
 #pragma once
 
 #include "detail/common.h"
+#include "detail/type_caster_base.h"
+#include "cast.h"
 #include "operators.h"
 
 #include <algorithm>
 #include <sstream>
+#include <type_traits>
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
@@ -58,9 +61,11 @@ struct is_comparable<
 /* For a vector/map data structure, recursively check the value type
    (which is std::pair for maps) */
 template <typename T>
-struct is_comparable<T, enable_if_t<container_traits<T>::is_vector>> {
-    static constexpr const bool value = is_comparable<typename T::value_type>::value;
-};
+struct is_comparable<T, enable_if_t<container_traits<T>::is_vector>>
+    : is_comparable<typename recursive_container_traits<T>::type_to_check_recursively> {};
+
+template <>
+struct is_comparable<recursive_bottom> : std::true_type {};
 
 /* For pairs, recursively check the two data types */
 template <typename T>
@@ -352,13 +357,17 @@ void vector_accessor(enable_if_t<vector_needs_copy<Vector>::value, Class_> &cl)
     using DiffType = typename Vector::difference_type;
     using ItType = typename Vector::iterator;
     cl.def("__getitem__", [](const Vector &v, DiffType i) -> T {
-        if (i < 0 && (i += v.size()) < 0) {
+        if (i < 0) {
+            i += v.size();
+            if (i < 0) {
+                throw index_error();
+            }
+        }
+        auto i_st = static_cast<SizeType>(i);
+        if (i_st >= v.size()) {
             throw index_error();
         }
-        if ((SizeType) i >= v.size()) {
-            throw index_error();
-        }
-        return v[(SizeType) i];
+        return v[i_st];
     });
 
     cl.def(
@@ -636,18 +645,52 @@ auto map_if_insertion_operator(Class_ &cl, std::string const &name)
         "Return the canonical string representation of this map.");
 }
 
-template <typename Map>
+template <typename KeyType>
 struct keys_view {
-    Map &map;
+    virtual size_t len() = 0;
+    virtual iterator iter() = 0;
+    virtual bool contains(const KeyType &k) = 0;
+    virtual bool contains(const object &k) = 0;
+    virtual ~keys_view() = default;
 };
 
-template <typename Map>
+template <typename MappedType>
 struct values_view {
+    virtual size_t len() = 0;
+    virtual iterator iter() = 0;
+    virtual ~values_view() = default;
+};
+
+template <typename KeyType, typename MappedType>
+struct items_view {
+    virtual size_t len() = 0;
+    virtual iterator iter() = 0;
+    virtual ~items_view() = default;
+};
+
+template <typename Map, typename KeysView>
+struct KeysViewImpl : public KeysView {
+    explicit KeysViewImpl(Map &map) : map(map) {}
+    size_t len() override { return map.size(); }
+    iterator iter() override { return make_key_iterator(map.begin(), map.end()); }
+    bool contains(const typename Map::key_type &k) override { return map.find(k) != map.end(); }
+    bool contains(const object &) override { return false; }
     Map &map;
 };
 
-template <typename Map>
-struct items_view {
+template <typename Map, typename ValuesView>
+struct ValuesViewImpl : public ValuesView {
+    explicit ValuesViewImpl(Map &map) : map(map) {}
+    size_t len() override { return map.size(); }
+    iterator iter() override { return make_value_iterator(map.begin(), map.end()); }
+    Map &map;
+};
+
+template <typename Map, typename ItemsView>
+struct ItemsViewImpl : public ItemsView {
+    explicit ItemsViewImpl(Map &map) : map(map) {}
+    size_t len() override { return map.size(); }
+    iterator iter() override { return make_iterator(map.begin(), map.end()); }
     Map &map;
 };
 
@@ -657,9 +700,11 @@ template <typename Map, typename holder_type = std::unique_ptr<Map>, typename...
 class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args &&...args) {
     using KeyType = typename Map::key_type;
     using MappedType = typename Map::mapped_type;
-    using KeysView = detail::keys_view<Map>;
-    using ValuesView = detail::values_view<Map>;
-    using ItemsView = detail::items_view<Map>;
+    using StrippedKeyType = detail::remove_cvref_t<KeyType>;
+    using StrippedMappedType = detail::remove_cvref_t<MappedType>;
+    using KeysView = detail::keys_view<StrippedKeyType>;
+    using ValuesView = detail::values_view<StrippedMappedType>;
+    using ItemsView = detail::items_view<StrippedKeyType, StrippedMappedType>;
     using Class_ = class_<Map, holder_type>;
 
     // If either type is a non-module-local bound type then make the map binding non-local as well;
@@ -673,12 +718,57 @@ class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args &&
     }
 
     Class_ cl(scope, name.c_str(), pybind11::module_local(local), std::forward<Args>(args)...);
-    class_<KeysView> keys_view(
-        scope, ("KeysView[" + name + "]").c_str(), pybind11::module_local(local));
-    class_<ValuesView> values_view(
-        scope, ("ValuesView[" + name + "]").c_str(), pybind11::module_local(local));
-    class_<ItemsView> items_view(
-        scope, ("ItemsView[" + name + "]").c_str(), pybind11::module_local(local));
+    static constexpr auto key_type_descr = detail::make_caster<KeyType>::name;
+    static constexpr auto mapped_type_descr = detail::make_caster<MappedType>::name;
+    std::string key_type_name(key_type_descr.text), mapped_type_name(mapped_type_descr.text);
+
+    // If key type isn't properly wrapped, fall back to C++ names
+    if (key_type_name == "%") {
+        key_type_name = detail::type_info_description(typeid(KeyType));
+    }
+    // Similarly for value type:
+    if (mapped_type_name == "%") {
+        mapped_type_name = detail::type_info_description(typeid(MappedType));
+    }
+
+    // Wrap KeysView[KeyType] if it wasn't already wrapped
+    if (!detail::get_type_info(typeid(KeysView))) {
+        class_<KeysView> keys_view(
+            scope, ("KeysView[" + key_type_name + "]").c_str(), pybind11::module_local(local));
+        keys_view.def("__len__", &KeysView::len);
+        keys_view.def("__iter__",
+                      &KeysView::iter,
+                      keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
+        );
+        keys_view.def("__contains__",
+                      static_cast<bool (KeysView::*)(const KeyType &)>(&KeysView::contains));
+        // Fallback for when the object is not of the key type
+        keys_view.def("__contains__",
+                      static_cast<bool (KeysView::*)(const object &)>(&KeysView::contains));
+    }
+    // Similarly for ValuesView:
+    if (!detail::get_type_info(typeid(ValuesView))) {
+        class_<ValuesView> values_view(scope,
+                                       ("ValuesView[" + mapped_type_name + "]").c_str(),
+                                       pybind11::module_local(local));
+        values_view.def("__len__", &ValuesView::len);
+        values_view.def("__iter__",
+                        &ValuesView::iter,
+                        keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
+        );
+    }
+    // Similarly for ItemsView:
+    if (!detail::get_type_info(typeid(ItemsView))) {
+        class_<ItemsView> items_view(
+            scope,
+            ("ItemsView[" + key_type_name + ", ").append(mapped_type_name + "]").c_str(),
+            pybind11::module_local(local));
+        items_view.def("__len__", &ItemsView::len);
+        items_view.def("__iter__",
+                       &ItemsView::iter,
+                       keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
+        );
+    }
 
     cl.def(init<>());
 
@@ -698,19 +788,25 @@ class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args &&
 
     cl.def(
         "keys",
-        [](Map &m) { return KeysView{m}; },
+        [](Map &m) {
+            return std::unique_ptr<KeysView>(new detail::KeysViewImpl<Map, KeysView>(m));
+        },
         keep_alive<0, 1>() /* Essential: keep map alive while view exists */
     );
 
     cl.def(
         "values",
-        [](Map &m) { return ValuesView{m}; },
+        [](Map &m) {
+            return std::unique_ptr<ValuesView>(new detail::ValuesViewImpl<Map, ValuesView>(m));
+        },
         keep_alive<0, 1>() /* Essential: keep map alive while view exists */
     );
 
     cl.def(
         "items",
-        [](Map &m) { return ItemsView{m}; },
+        [](Map &m) {
+            return std::unique_ptr<ItemsView>(new detail::ItemsViewImpl<Map, ItemsView>(m));
+        },
         keep_alive<0, 1>() /* Essential: keep map alive while view exists */
     );
 
@@ -749,36 +845,6 @@ class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args &&
 
     cl.def("__len__", &Map::size);
 
-    keys_view.def("__len__", [](KeysView &view) { return view.map.size(); });
-    keys_view.def(
-        "__iter__",
-        [](KeysView &view) { return make_key_iterator(view.map.begin(), view.map.end()); },
-        keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
-    );
-    keys_view.def("__contains__", [](KeysView &view, const KeyType &k) -> bool {
-        auto it = view.map.find(k);
-        if (it == view.map.end()) {
-            return false;
-        }
-        return true;
-    });
-    // Fallback for when the object is not of the key type
-    keys_view.def("__contains__", [](KeysView &, const object &) -> bool { return false; });
-
-    values_view.def("__len__", [](ValuesView &view) { return view.map.size(); });
-    values_view.def(
-        "__iter__",
-        [](ValuesView &view) { return make_value_iterator(view.map.begin(), view.map.end()); },
-        keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
-    );
-
-    items_view.def("__len__", [](ItemsView &view) { return view.map.size(); });
-    items_view.def(
-        "__iter__",
-        [](ItemsView &view) { return make_iterator(view.map.begin(), view.map.end()); },
-        keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
-    );
-
     return cl;
 }
 
diff --git a/wrap/pybind11/include/pybind11/type_caster_pyobject_ptr.h b/wrap/pybind11/include/pybind11/type_caster_pyobject_ptr.h
new file mode 100644
index 000000000..aa914f9e1
--- /dev/null
+++ b/wrap/pybind11/include/pybind11/type_caster_pyobject_ptr.h
@@ -0,0 +1,61 @@
+// Copyright (c) 2023 The pybind Community.
+
+#pragma once
+
+#include "detail/common.h"
+#include "detail/descr.h"
+#include "cast.h"
+#include "pytypes.h"
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+template <>
+class type_caster<PyObject> {
+public:
+    static constexpr auto name = const_name("object"); // See discussion under PR #4601.
+
+    // This overload is purely to guard against accidents.
+    template <typename T,
+              detail::enable_if_t<!is_same_ignoring_cvref<T, PyObject *>::value, int> = 0>
+    static handle cast(T &&, return_value_policy, handle /*parent*/) {
+        static_assert(is_same_ignoring_cvref<T, PyObject *>::value,
+                      "Invalid C++ type T for to-Python conversion (type_caster<PyObject>).");
+        return nullptr; // Unreachable.
+    }
+
+    static handle cast(PyObject *src, return_value_policy policy, handle /*parent*/) {
+        if (src == nullptr) {
+            throw error_already_set();
+        }
+        if (PyErr_Occurred()) {
+            raise_from(PyExc_SystemError, "src != nullptr but PyErr_Occurred()");
+            throw error_already_set();
+        }
+        if (policy == return_value_policy::take_ownership) {
+            return src;
+        }
+        if (policy == return_value_policy::reference
+            || policy == return_value_policy::automatic_reference) {
+            return handle(src).inc_ref();
+        }
+        pybind11_fail("type_caster<PyObject>::cast(): unsupported return_value_policy: "
+                      + std::to_string(static_cast<int>(policy)));
+    }
+
+    bool load(handle src, bool) {
+        value = reinterpret_borrow<object>(src);
+        return true;
+    }
+
+    template <typename T>
+    using cast_op_type = PyObject *;
+
+    explicit operator PyObject *() { return value.ptr(); }
+
+private:
+    object value;
+};
+
+PYBIND11_NAMESPACE_END(detail)
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
diff --git a/wrap/pybind11/noxfile.py b/wrap/pybind11/noxfile.py
index fe36d70fe..021ced245 100644
--- a/wrap/pybind11/noxfile.py
+++ b/wrap/pybind11/noxfile.py
@@ -5,7 +5,17 @@ import nox
 nox.needs_version = ">=2022.1.7"
 nox.options.sessions = ["lint", "tests", "tests_packaging"]
 
-PYTHON_VERISONS = ["3.6", "3.7", "3.8", "3.9", "3.10", "3.11", "pypy3.7", "pypy3.8"]
+PYTHON_VERSIONS = [
+    "3.6",
+    "3.7",
+    "3.8",
+    "3.9",
+    "3.10",
+    "3.11",
+    "pypy3.7",
+    "pypy3.8",
+    "pypy3.9",
+]
 
 if os.environ.get("CI", None):
     nox.options.error_on_missing_interpreters = True
@@ -17,10 +27,10 @@ def lint(session: nox.Session) -> None:
     Lint the codebase (except for clang-format/tidy).
     """
     session.install("pre-commit")
-    session.run("pre-commit", "run", "-a")
+    session.run("pre-commit", "run", "-a", *session.posargs)
 
 
-@nox.session(python=PYTHON_VERISONS)
+@nox.session(python=PYTHON_VERSIONS)
 def tests(session: nox.Session) -> None:
     """
     Run the tests (requires a compiler).
@@ -48,7 +58,7 @@ def tests_packaging(session: nox.Session) -> None:
     """
 
     session.install("-r", "tests/requirements.txt", "--prefer-binary")
-    session.run("pytest", "tests/extra_python_package")
+    session.run("pytest", "tests/extra_python_package", *session.posargs)
 
 
 @nox.session(reuse_venv=True)
diff --git a/wrap/pybind11/pybind11/__init__.py b/wrap/pybind11/pybind11/__init__.py
index a1be96981..7c10b3057 100644
--- a/wrap/pybind11/pybind11/__init__.py
+++ b/wrap/pybind11/pybind11/__init__.py
@@ -1,16 +1,17 @@
 import sys
 
-if sys.version_info < (3, 6):
+if sys.version_info < (3, 6):  # noqa: UP036
     msg = "pybind11 does not support Python < 3.6. 2.9 was the last release supporting Python 2.7 and 3.5."
     raise ImportError(msg)
 
 
 from ._version import __version__, version_info
-from .commands import get_cmake_dir, get_include
+from .commands import get_cmake_dir, get_include, get_pkgconfig_dir
 
 __all__ = (
     "version_info",
     "__version__",
     "get_include",
     "get_cmake_dir",
+    "get_pkgconfig_dir",
 )
diff --git a/wrap/pybind11/pybind11/__main__.py b/wrap/pybind11/pybind11/__main__.py
index 22fc4471e..180665c23 100644
--- a/wrap/pybind11/pybind11/__main__.py
+++ b/wrap/pybind11/pybind11/__main__.py
@@ -4,7 +4,8 @@ import argparse
 import sys
 import sysconfig
 
-from .commands import get_cmake_dir, get_include
+from ._version import __version__
+from .commands import get_cmake_dir, get_include, get_pkgconfig_dir
 
 
 def print_includes() -> None:
@@ -24,8 +25,13 @@ def print_includes() -> None:
 
 
 def main() -> None:
-
     parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "--version",
+        action="version",
+        version=__version__,
+        help="Print the version and exit.",
+    )
     parser.add_argument(
         "--includes",
         action="store_true",
@@ -36,6 +42,11 @@ def main() -> None:
         action="store_true",
         help="Print the CMake module directory, ideal for setting -Dpybind11_ROOT in CMake.",
     )
+    parser.add_argument(
+        "--pkgconfigdir",
+        action="store_true",
+        help="Print the pkgconfig directory, ideal for setting $PKG_CONFIG_PATH.",
+    )
     args = parser.parse_args()
     if not sys.argv[1:]:
         parser.print_help()
@@ -43,6 +54,8 @@ def main() -> None:
         print_includes()
     if args.cmakedir:
         print(get_cmake_dir())
+    if args.pkgconfigdir:
+        print(get_pkgconfig_dir())
 
 
 if __name__ == "__main__":
diff --git a/wrap/pybind11/pybind11/_version.py b/wrap/pybind11/pybind11/_version.py
index b78d5963d..9280fa054 100644
--- a/wrap/pybind11/pybind11/_version.py
+++ b/wrap/pybind11/pybind11/_version.py
@@ -8,5 +8,5 @@ def _to_int(s: str) -> Union[int, str]:
         return s
 
 
-__version__ = "2.10.0"
+__version__ = "2.11.1"
 version_info = tuple(_to_int(s) for s in __version__.split("."))
diff --git a/wrap/pybind11/pybind11/commands.py b/wrap/pybind11/pybind11/commands.py
index a29c8ca61..b11690f46 100644
--- a/wrap/pybind11/pybind11/commands.py
+++ b/wrap/pybind11/pybind11/commands.py
@@ -3,7 +3,7 @@ import os
 DIR = os.path.abspath(os.path.dirname(__file__))
 
 
-def get_include(user: bool = False) -> str:  # pylint: disable=unused-argument
+def get_include(user: bool = False) -> str:  # noqa: ARG001
     """
     Return the path to the pybind11 include directory. The historical "user"
     argument is unused, and may be removed.
@@ -23,3 +23,15 @@ def get_cmake_dir() -> str:
 
     msg = "pybind11 not installed, installation required to access the CMake files"
     raise ImportError(msg)
+
+
+def get_pkgconfig_dir() -> str:
+    """
+    Return the path to the pybind11 pkgconfig directory.
+    """
+    pkgconfig_installed_path = os.path.join(DIR, "share", "pkgconfig")
+    if os.path.exists(pkgconfig_installed_path):
+        return pkgconfig_installed_path
+
+    msg = "pybind11 not installed, installation required to access the pkgconfig files"
+    raise ImportError(msg)
diff --git a/wrap/pybind11/pybind11/setup_helpers.py b/wrap/pybind11/pybind11/setup_helpers.py
index 1fd04b915..aeeee9dcf 100644
--- a/wrap/pybind11/pybind11/setup_helpers.py
+++ b/wrap/pybind11/pybind11/setup_helpers.py
@@ -66,8 +66,8 @@ try:
     from setuptools import Extension as _Extension
     from setuptools.command.build_ext import build_ext as _build_ext
 except ImportError:
-    from distutils.command.build_ext import build_ext as _build_ext
-    from distutils.extension import Extension as _Extension
+    from distutils.command.build_ext import build_ext as _build_ext  # type: ignore[assignment]
+    from distutils.extension import Extension as _Extension  # type: ignore[assignment]
 
 import distutils.ccompiler
 import distutils.errors
@@ -84,7 +84,7 @@ STD_TMPL = "/std:c++{}" if WIN else "-std=c++{}"
 # directory into your path if it sits beside your setup.py.
 
 
-class Pybind11Extension(_Extension):  # type: ignore[misc]
+class Pybind11Extension(_Extension):
     """
     Build a C++11+ Extension module with pybind11. This automatically adds the
     recommended flags when you init the extension and assumes C++ sources - you
@@ -118,7 +118,6 @@ class Pybind11Extension(_Extension):  # type: ignore[misc]
         self.extra_link_args[:0] = flags
 
     def __init__(self, *args: Any, **kwargs: Any) -> None:
-
         self._cxx_level = 0
         cxx_std = kwargs.pop("cxx_std", 0)
 
@@ -145,7 +144,6 @@ class Pybind11Extension(_Extension):  # type: ignore[misc]
         self.cxx_std = cxx_std
 
         cflags = []
-        ldflags = []
         if WIN:
             cflags += ["/EHsc", "/bigobj"]
         else:
@@ -155,11 +153,7 @@ class Pybind11Extension(_Extension):  # type: ignore[misc]
             c_cpp_flags = shlex.split(env_cflags) + shlex.split(env_cppflags)
             if not any(opt.startswith("-g") for opt in c_cpp_flags):
                 cflags += ["-g0"]
-            if MACOS:
-                cflags += ["-stdlib=libc++"]
-                ldflags += ["-stdlib=libc++"]
         self._add_cflags(cflags)
-        self._add_ldflags(ldflags)
 
     @property
     def cxx_std(self) -> int:
@@ -174,9 +168,10 @@ class Pybind11Extension(_Extension):  # type: ignore[misc]
 
     @cxx_std.setter
     def cxx_std(self, level: int) -> None:
-
         if self._cxx_level:
-            warnings.warn("You cannot safely change the cxx_level after setting it!")
+            warnings.warn(
+                "You cannot safely change the cxx_level after setting it!", stacklevel=2
+            )
 
         # MSVC 2015 Update 3 and later only have 14 (and later 17) modes, so
         # force a valid flag here.
@@ -271,7 +266,7 @@ def auto_cpp_level(compiler: Any) -> Union[str, int]:
     raise RuntimeError(msg)
 
 
-class build_ext(_build_ext):  # type: ignore[misc] # noqa: N801
+class build_ext(_build_ext):  # noqa: N801
     """
     Customized build_ext that allows an auto-search for the highest supported
     C++ level for Pybind11Extension. This is only needed for the auto-search
@@ -341,7 +336,7 @@ def naive_recompile(obj: str, src: str) -> bool:
     return os.stat(obj).st_mtime < os.stat(src).st_mtime
 
 
-def no_recompile(obg: str, src: str) -> bool:  # pylint: disable=unused-argument
+def no_recompile(obg: str, src: str) -> bool:  # noqa: ARG001
     """
     This is the safest but slowest choice (and is the default) - will always
     recompile sources.
@@ -439,7 +434,6 @@ class ParallelCompile:
             extra_postargs: Optional[List[str]] = None,
             depends: Optional[List[str]] = None,
         ) -> Any:
-
             # These lines are directly from distutils.ccompiler.CCompiler
             macros, objects, extra_postargs, pp_opts, build = compiler._setup_compile(  # type: ignore[attr-defined]
                 output_dir, macros, include_dirs, sources, depends, extra_postargs
diff --git a/wrap/pybind11/pyproject.toml b/wrap/pybind11/pyproject.toml
index 3ba1b4b22..59c15ea63 100644
--- a/wrap/pybind11/pyproject.toml
+++ b/wrap/pybind11/pyproject.toml
@@ -2,6 +2,7 @@
 requires = ["setuptools>=42", "cmake>=3.18", "ninja"]
 build-backend = "setuptools.build_meta"
 
+
 [tool.check-manifest]
 ignore = [
     "tests/**",
@@ -15,11 +16,6 @@ ignore = [
     "noxfile.py",
 ]
 
-[tool.isort]
-# Needs the compiled .so modules and env.py from tests
-known_first_party = "env,pybind11_cross_module_tests,pybind11_tests,"
-# For black compatibility
-profile = "black"
 
 [tool.mypy]
 files = ["pybind11"]
@@ -30,7 +26,7 @@ enable_error_code = ["ignore-without-code", "redundant-expr", "truthy-bool"]
 warn_unreachable = true
 
 [[tool.mypy.overrides]]
-module = ["ghapi.*", "setuptools.*"]
+module = ["ghapi.*"]
 ignore_missing_imports = true
 
 
@@ -58,4 +54,45 @@ messages_control.disable = [
   "invalid-name",
   "protected-access",
   "missing-module-docstring",
+  "unused-argument",  # covered by Ruff ARG
 ]
+
+
+[tool.ruff]
+select = [
+  "E", "F", "W", # flake8
+  "B",           # flake8-bugbear
+  "I",           # isort
+  "N",           # pep8-naming
+  "ARG",         # flake8-unused-arguments
+  "C4",          # flake8-comprehensions
+  "EM",          # flake8-errmsg
+  "ICN",         # flake8-import-conventions
+  "ISC",         # flake8-implicit-str-concat
+  "PGH",         # pygrep-hooks
+  "PIE",         # flake8-pie
+  "PL",          # pylint
+  "PT",          # flake8-pytest-style
+  "RET",         # flake8-return
+  "RUF100",      # Ruff-specific
+  "SIM",         # flake8-simplify
+  "UP",          # pyupgrade
+  "YTT",         # flake8-2020
+]
+ignore = [
+  "PLR",    # Design related pylint
+  "E501",   # Line too long (Black is enough)
+  "PT011",  # Too broad with raises in pytest
+  "PT004",  # Fixture that doesn't return needs underscore (no, it is fine)
+  "SIM118", # iter(x) is not always the same as iter(x.keys())
+]
+target-version = "py37"
+src = ["src"]
+unfixable = ["T20"]
+exclude = []
+line-length = 120
+isort.known-first-party = ["env", "pybind11_cross_module_tests", "pybind11_tests"]
+
+[tool.ruff.per-file-ignores]
+"tests/**" = ["EM", "N"]
+"tests/test_call_policies.py" = ["PLC1901"]
diff --git a/wrap/pybind11/setup.cfg b/wrap/pybind11/setup.cfg
index 36fbfed4f..92e6c953a 100644
--- a/wrap/pybind11/setup.cfg
+++ b/wrap/pybind11/setup.cfg
@@ -20,6 +20,7 @@ classifiers =
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11
+    Programming Language :: Python :: 3.12
     License :: OSI Approved :: BSD License
     Programming Language :: Python :: Implementation :: PyPy
     Programming Language :: Python :: Implementation :: CPython
@@ -40,11 +41,3 @@ project_urls =
 [options]
 python_requires = >=3.6
 zip_safe = False
-
-
-[flake8]
-max-line-length = 120
-show_source = True
-exclude = .git, __pycache__, build, dist, docs, tools, venv
-extend-ignore = E203, E722, B950
-extend-select = B9
diff --git a/wrap/pybind11/setup.py b/wrap/pybind11/setup.py
index a149755bf..9fea7d35c 100644
--- a/wrap/pybind11/setup.py
+++ b/wrap/pybind11/setup.py
@@ -96,7 +96,7 @@ def get_and_replace(
 
 # Use our input files instead when making the SDist (and anything that depends
 # on it, like a wheel)
-class SDist(setuptools.command.sdist.sdist):  # type: ignore[misc]
+class SDist(setuptools.command.sdist.sdist):
     def make_release_tree(self, base_dir: str, files: List[str]) -> None:
         super().make_release_tree(base_dir, files)
 
@@ -127,6 +127,7 @@ with remove_output("pybind11/include", "pybind11/share"):
             "-DCMAKE_INSTALL_PREFIX=pybind11",
             "-DBUILD_TESTING=OFF",
             "-DPYBIND11_NOPYTHON=ON",
+            "-Dprefix_for_pc_file=${pcfiledir}/../../",
         ]
         if "CMAKE_ARGS" in os.environ:
             fcommand = [
diff --git a/wrap/pybind11/tests/CMakeLists.txt b/wrap/pybind11/tests/CMakeLists.txt
index 7296cd1b8..80ee9c1f1 100644
--- a/wrap/pybind11/tests/CMakeLists.txt
+++ b/wrap/pybind11/tests/CMakeLists.txt
@@ -5,20 +5,17 @@
 # All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
-cmake_minimum_required(VERSION 3.4)
+cmake_minimum_required(VERSION 3.5)
 
-# The `cmake_minimum_required(VERSION 3.4...3.18)` syntax does not work with
+# The `cmake_minimum_required(VERSION 3.5...3.26)` syntax does not work with
 # some versions of VS that have a patched CMake 3.11. This forces us to emulate
 # the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.21)
+if(${CMAKE_VERSION} VERSION_LESS 3.26)
   cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
-  cmake_policy(VERSION 3.21)
+  cmake_policy(VERSION 3.26)
 endif()
 
-# Only needed for CMake < 3.5 support
-include(CMakeParseArguments)
-
 # Filter out items; print an optional message if any items filtered. This ignores extensions.
 #
 # Usage:
@@ -128,7 +125,8 @@ set(PYBIND11_TEST_FILES
     test_custom_type_casters
     test_custom_type_setup
     test_docstring_options
-    test_eigen
+    test_eigen_matrix
+    test_eigen_tensor
     test_enum
     test_eval
     test_exceptions
@@ -153,7 +151,11 @@ set(PYBIND11_TEST_FILES
     test_stl_binders
     test_tagbased_polymorphic
     test_thread
+    test_type_caster_pyobject_ptr
     test_union
+    test_unnamed_namespace_a
+    test_unnamed_namespace_b
+    test_vector_unique_ptr_member
     test_virtual_functions)
 
 # Invoking cmake with something like:
@@ -168,7 +170,7 @@ if(PYBIND11_TEST_OVERRIDE)
   # This allows the override to be done with extensions, preserving backwards compatibility.
   foreach(test_name ${TEST_FILES_NO_EXT})
     if(NOT ${test_name} IN_LIST TEST_OVERRIDE_NO_EXT
-    )# If not in the whitelist, add to be filtered out.
+    )# If not in the allowlist, add to be filtered out.
       list(APPEND PYBIND11_TEST_FILTER ${test_name})
     endif()
   endforeach()
@@ -233,7 +235,10 @@ list(GET PYBIND11_EIGEN_VERSION_AND_HASH 1 PYBIND11_EIGEN_VERSION_HASH)
 # Check if Eigen is available; if not, remove from PYBIND11_TEST_FILES (but
 # keep it in PYBIND11_PYTEST_FILES, so that we get the "eigen is not installed"
 # skip message).
-list(FIND PYBIND11_TEST_FILES test_eigen.cpp PYBIND11_TEST_FILES_EIGEN_I)
+list(FIND PYBIND11_TEST_FILES test_eigen_matrix.cpp PYBIND11_TEST_FILES_EIGEN_I)
+if(PYBIND11_TEST_FILES_EIGEN_I EQUAL -1)
+  list(FIND PYBIND11_TEST_FILES test_eigen_tensor.cpp PYBIND11_TEST_FILES_EIGEN_I)
+endif()
 if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
   # Try loading via newer Eigen's Eigen3Config first (bypassing tools/FindEigen3.cmake).
   # Eigen 3.3.1+ exports a cmake 3.0+ target for handling dependency requirements, but also
@@ -288,13 +293,34 @@ if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
       set(EIGEN3_VERSION ${EIGEN3_VERSION_STRING})
     endif()
     message(STATUS "Building tests with Eigen v${EIGEN3_VERSION}")
+
+    if(NOT (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0))
+      tests_extra_targets("test_eigen_tensor.py" "eigen_tensor_avoid_stl_array")
+    endif()
+
   else()
-    list(REMOVE_AT PYBIND11_TEST_FILES ${PYBIND11_TEST_FILES_EIGEN_I})
+    list(FIND PYBIND11_TEST_FILES test_eigen_matrix.cpp PYBIND11_TEST_FILES_EIGEN_I)
+    if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
+      list(REMOVE_AT PYBIND11_TEST_FILES ${PYBIND11_TEST_FILES_EIGEN_I})
+    endif()
+
+    list(FIND PYBIND11_TEST_FILES test_eigen_tensor.cpp PYBIND11_TEST_FILES_EIGEN_I)
+    if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
+      list(REMOVE_AT PYBIND11_TEST_FILES ${PYBIND11_TEST_FILES_EIGEN_I})
+    endif()
     message(
       STATUS "Building tests WITHOUT Eigen, use -DDOWNLOAD_EIGEN=ON on CMake 3.11+ to download")
   endif()
 endif()
 
+# Some code doesn't support gcc 4
+if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0)
+  list(FIND PYBIND11_TEST_FILES test_eigen_tensor.cpp PYBIND11_TEST_FILES_EIGEN_I)
+  if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
+    list(REMOVE_AT PYBIND11_TEST_FILES ${PYBIND11_TEST_FILES_EIGEN_I})
+  endif()
+endif()
+
 # Optional dependency for some tests (boost::variant is only supported with version >= 1.56)
 find_package(Boost 1.56)
 
diff --git a/wrap/pybind11/tests/conftest.py b/wrap/pybind11/tests/conftest.py
index 02ce263af..ad5b47b4b 100644
--- a/wrap/pybind11/tests/conftest.py
+++ b/wrap/pybind11/tests/conftest.py
@@ -7,13 +7,36 @@ Adds docstring and exceptions message sanitizers.
 import contextlib
 import difflib
 import gc
+import multiprocessing
 import re
+import sys
 import textwrap
+import traceback
 
 import pytest
 
 # Early diagnostic for failed imports
-import pybind11_tests
+try:
+    import pybind11_tests
+except Exception:
+    # pytest does not show the traceback without this.
+    traceback.print_exc()
+    raise
+
+
+@pytest.fixture(scope="session", autouse=True)
+def use_multiprocessing_forkserver_on_linux():
+    if sys.platform != "linux":
+        # The default on Windows and macOS is "spawn": If it's not broken, don't fix it.
+        return
+
+    # Full background: https://github.com/pybind/pybind11/issues/4105#issuecomment-1301004592
+    # In a nutshell: fork() after starting threads == flakiness in the form of deadlocks.
+    # It is actually a well-known pitfall, unfortunately without guard rails.
+    # "forkserver" is more performant than "spawn" (~9s vs ~13s for tests/test_gil_scoped.py,
+    # visit the issuecomment link above for details).
+    multiprocessing.set_start_method("forkserver")
+
 
 _long_marker = re.compile(r"([0-9])L")
 _hexadecimal = re.compile(r"0x[0-9a-fA-F]+")
@@ -59,9 +82,8 @@ class Output:
         b = _strip_and_dedent(other).splitlines()
         if a == b:
             return True
-        else:
-            self.explanation = _make_explanation(a, b)
-            return False
+        self.explanation = _make_explanation(a, b)
+        return False
 
 
 class Unordered(Output):
@@ -72,9 +94,8 @@ class Unordered(Output):
         b = _split_and_sort(other)
         if a == b:
             return True
-        else:
-            self.explanation = _make_explanation(a, b)
-            return False
+        self.explanation = _make_explanation(a, b)
+        return False
 
 
 class Capture:
@@ -95,9 +116,8 @@ class Capture:
         b = other
         if a == b:
             return True
-        else:
-            self.explanation = a.explanation
-            return False
+        self.explanation = a.explanation
+        return False
 
     def __str__(self):
         return self.out
@@ -114,7 +134,7 @@ class Capture:
         return Output(self.err)
 
 
-@pytest.fixture
+@pytest.fixture()
 def capture(capsys):
     """Extended `capsys` with context manager and custom equality operators"""
     return Capture(capsys)
@@ -135,25 +155,22 @@ class SanitizedString:
         b = _strip_and_dedent(other)
         if a == b:
             return True
-        else:
-            self.explanation = _make_explanation(a.splitlines(), b.splitlines())
-            return False
+        self.explanation = _make_explanation(a.splitlines(), b.splitlines())
+        return False
 
 
 def _sanitize_general(s):
     s = s.strip()
     s = s.replace("pybind11_tests.", "m.")
-    s = _long_marker.sub(r"\1", s)
-    return s
+    return _long_marker.sub(r"\1", s)
 
 
 def _sanitize_docstring(thing):
     s = thing.__doc__
-    s = _sanitize_general(s)
-    return s
+    return _sanitize_general(s)
 
 
-@pytest.fixture
+@pytest.fixture()
 def doc():
     """Sanitize docstrings and add custom failure explanation"""
     return SanitizedString(_sanitize_docstring)
@@ -162,30 +179,20 @@ def doc():
 def _sanitize_message(thing):
     s = str(thing)
     s = _sanitize_general(s)
-    s = _hexadecimal.sub("0", s)
-    return s
+    return _hexadecimal.sub("0", s)
 
 
-@pytest.fixture
+@pytest.fixture()
 def msg():
     """Sanitize messages and add custom failure explanation"""
     return SanitizedString(_sanitize_message)
 
 
-# noinspection PyUnusedLocal
-def pytest_assertrepr_compare(op, left, right):
+def pytest_assertrepr_compare(op, left, right):  # noqa: ARG001
     """Hook to insert custom failure explanation"""
     if hasattr(left, "explanation"):
         return left.explanation
-
-
-@contextlib.contextmanager
-def suppress(exception):
-    """Suppress the desired exception"""
-    try:
-        yield
-    except exception:
-        pass
+    return None
 
 
 def gc_collect():
@@ -196,7 +203,7 @@ def gc_collect():
 
 
 def pytest_configure():
-    pytest.suppress = suppress
+    pytest.suppress = contextlib.suppress
     pytest.gc_collect = gc_collect
 
 
@@ -210,4 +217,5 @@ def pytest_report_header(config):
         f" {pybind11_tests.compiler_info}"
         f" {pybind11_tests.cpp_std}"
         f" {pybind11_tests.PYBIND11_INTERNALS_ID}"
+        f" PYBIND11_SIMPLE_GIL_MANAGEMENT={pybind11_tests.PYBIND11_SIMPLE_GIL_MANAGEMENT}"
     )
diff --git a/wrap/pybind11/tests/constructor_stats.h b/wrap/pybind11/tests/constructor_stats.h
index a3835c21e..937f6c233 100644
--- a/wrap/pybind11/tests/constructor_stats.h
+++ b/wrap/pybind11/tests/constructor_stats.h
@@ -115,7 +115,7 @@ public:
 #if defined(PYPY_VERSION)
         PyObject *globals = PyEval_GetGlobals();
         PyObject *result = PyRun_String("import gc\n"
-                                        "for i in range(2):"
+                                        "for i in range(2):\n"
                                         "    gc.collect()\n",
                                         Py_file_input,
                                         globals,
diff --git a/wrap/pybind11/tests/cross_module_gil_utils.cpp b/wrap/pybind11/tests/cross_module_gil_utils.cpp
index 1436c35d6..7c20849dd 100644
--- a/wrap/pybind11/tests/cross_module_gil_utils.cpp
+++ b/wrap/pybind11/tests/cross_module_gil_utils.cpp
@@ -6,9 +6,15 @@
     All rights reserved. Use of this source code is governed by a
     BSD-style license that can be found in the LICENSE file.
 */
+#if defined(PYBIND11_INTERNALS_VERSION)
+#    undef PYBIND11_INTERNALS_VERSION
+#endif
+#define PYBIND11_INTERNALS_VERSION 21814642 // Ensure this module has its own `internals` instance.
 #include <pybind11/pybind11.h>
 
 #include <cstdint>
+#include <string>
+#include <thread>
 
 // This file mimics a DSO that makes pybind11 calls but does not define a
 // PYBIND11_MODULE. The purpose is to test that such a DSO can create a
@@ -21,8 +27,54 @@
 namespace {
 
 namespace py = pybind11;
+
 void gil_acquire() { py::gil_scoped_acquire gil; }
 
+std::string gil_multi_acquire_release(unsigned bits) {
+    if ((bits & 0x1u) != 0u) {
+        py::gil_scoped_acquire gil;
+    }
+    if ((bits & 0x2u) != 0u) {
+        py::gil_scoped_release gil;
+    }
+    if ((bits & 0x4u) != 0u) {
+        py::gil_scoped_acquire gil;
+    }
+    if ((bits & 0x8u) != 0u) {
+        py::gil_scoped_release gil;
+    }
+    return PYBIND11_INTERNALS_ID;
+}
+
+struct CustomAutoGIL {
+    CustomAutoGIL() : gstate(PyGILState_Ensure()) {}
+    ~CustomAutoGIL() { PyGILState_Release(gstate); }
+
+    PyGILState_STATE gstate;
+};
+struct CustomAutoNoGIL {
+    CustomAutoNoGIL() : save(PyEval_SaveThread()) {}
+    ~CustomAutoNoGIL() { PyEval_RestoreThread(save); }
+
+    PyThreadState *save;
+};
+
+template <typename Acquire, typename Release>
+void gil_acquire_inner() {
+    Acquire acquire_outer;
+    Acquire acquire_inner;
+    Release release;
+}
+
+template <typename Acquire, typename Release>
+void gil_acquire_nested() {
+    Acquire acquire_outer;
+    Acquire acquire_inner;
+    Release release;
+    auto thread = std::thread(&gil_acquire_inner<Acquire, Release>);
+    thread.join();
+}
+
 constexpr char kModuleName[] = "cross_module_gil_utils";
 
 struct PyModuleDef moduledef = {
@@ -30,6 +82,9 @@ struct PyModuleDef moduledef = {
 
 } // namespace
 
+#define ADD_FUNCTION(Name, ...)                                                                   \
+    PyModule_AddObject(m, Name, PyLong_FromVoidPtr(reinterpret_cast<void *>(&__VA_ARGS__)));
+
 extern "C" PYBIND11_EXPORT PyObject *PyInit_cross_module_gil_utils() {
 
     PyObject *m = PyModule_Create(&moduledef);
@@ -37,8 +92,16 @@ extern "C" PYBIND11_EXPORT PyObject *PyInit_cross_module_gil_utils() {
     if (m != nullptr) {
         static_assert(sizeof(&gil_acquire) == sizeof(void *),
                       "Function pointer must have the same size as void*");
-        PyModule_AddObject(
-            m, "gil_acquire_funcaddr", PyLong_FromVoidPtr(reinterpret_cast<void *>(&gil_acquire)));
+        ADD_FUNCTION("gil_acquire_funcaddr", gil_acquire)
+        ADD_FUNCTION("gil_multi_acquire_release_funcaddr", gil_multi_acquire_release)
+        ADD_FUNCTION("gil_acquire_inner_custom_funcaddr",
+                     gil_acquire_inner<CustomAutoGIL, CustomAutoNoGIL>)
+        ADD_FUNCTION("gil_acquire_nested_custom_funcaddr",
+                     gil_acquire_nested<CustomAutoGIL, CustomAutoNoGIL>)
+        ADD_FUNCTION("gil_acquire_inner_pybind11_funcaddr",
+                     gil_acquire_inner<py::gil_scoped_acquire, py::gil_scoped_release>)
+        ADD_FUNCTION("gil_acquire_nested_pybind11_funcaddr",
+                     gil_acquire_nested<py::gil_scoped_acquire, py::gil_scoped_release>)
     }
 
     return m;
diff --git a/wrap/pybind11/tests/eigen_tensor_avoid_stl_array.cpp b/wrap/pybind11/tests/eigen_tensor_avoid_stl_array.cpp
new file mode 100644
index 000000000..eacc9e9bd
--- /dev/null
+++ b/wrap/pybind11/tests/eigen_tensor_avoid_stl_array.cpp
@@ -0,0 +1,14 @@
+/*
+    tests/eigen_tensor.cpp -- automatic conversion of Eigen Tensor
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#ifndef EIGEN_AVOID_STL_ARRAY
+#    define EIGEN_AVOID_STL_ARRAY
+#endif
+
+#include "test_eigen_tensor.inl"
+
+PYBIND11_MODULE(eigen_tensor_avoid_stl_array, m) { eigen_tensor_test::test_module(m); }
diff --git a/wrap/pybind11/tests/env.py b/wrap/pybind11/tests/env.py
index 0345df65d..7eea5a3b3 100644
--- a/wrap/pybind11/tests/env.py
+++ b/wrap/pybind11/tests/env.py
@@ -24,5 +24,4 @@ def deprecated_call():
     pytest_major_minor = (int(pieces[0]), int(pieces[1]))
     if pytest_major_minor < (3, 9):
         return pytest.warns((DeprecationWarning, PendingDeprecationWarning))
-    else:
-        return pytest.deprecated_call()
+    return pytest.deprecated_call()
diff --git a/wrap/pybind11/tests/extra_python_package/test_files.py b/wrap/pybind11/tests/extra_python_package/test_files.py
index ba16b5224..57387dd8b 100644
--- a/wrap/pybind11/tests/extra_python_package/test_files.py
+++ b/wrap/pybind11/tests/extra_python_package/test_files.py
@@ -12,6 +12,16 @@ import zipfile
 DIR = os.path.abspath(os.path.dirname(__file__))
 MAIN_DIR = os.path.dirname(os.path.dirname(DIR))
 
+PKGCONFIG = """\
+prefix=${{pcfiledir}}/../../
+includedir=${{prefix}}/include
+
+Name: pybind11
+Description: Seamless operability between C++11 and Python
+Version: {VERSION}
+Cflags: -I${{includedir}}
+"""
+
 
 main_headers = {
     "include/pybind11/attr.h",
@@ -33,6 +43,7 @@ main_headers = {
     "include/pybind11/pytypes.h",
     "include/pybind11/stl.h",
     "include/pybind11/stl_bind.h",
+    "include/pybind11/type_caster_pyobject_ptr.h",
 }
 
 detail_headers = {
@@ -45,6 +56,12 @@ detail_headers = {
     "include/pybind11/detail/typeid.h",
 }
 
+eigen_headers = {
+    "include/pybind11/eigen/common.h",
+    "include/pybind11/eigen/matrix.h",
+    "include/pybind11/eigen/tensor.h",
+}
+
 stl_headers = {
     "include/pybind11/stl/filesystem.h",
 }
@@ -59,6 +76,10 @@ cmake_files = {
     "share/cmake/pybind11/pybind11Tools.cmake",
 }
 
+pkgconfig_files = {
+    "share/pkgconfig/pybind11.pc",
+}
+
 py_files = {
     "__init__.py",
     "__main__.py",
@@ -68,8 +89,8 @@ py_files = {
     "setup_helpers.py",
 }
 
-headers = main_headers | detail_headers | stl_headers
-src_files = headers | cmake_files
+headers = main_headers | detail_headers | eigen_headers | stl_headers
+src_files = headers | cmake_files | pkgconfig_files
 all_files = src_files | py_files
 
 
@@ -78,10 +99,12 @@ sdist_files = {
     "pybind11/include",
     "pybind11/include/pybind11",
     "pybind11/include/pybind11/detail",
+    "pybind11/include/pybind11/eigen",
     "pybind11/include/pybind11/stl",
     "pybind11/share",
     "pybind11/share/cmake",
     "pybind11/share/cmake/pybind11",
+    "pybind11/share/pkgconfig",
     "pyproject.toml",
     "setup.cfg",
     "setup.py",
@@ -89,6 +112,7 @@ sdist_files = {
     "MANIFEST.in",
     "README.rst",
     "PKG-INFO",
+    "SECURITY.md",
 }
 
 local_sdist_files = {
@@ -101,22 +125,24 @@ local_sdist_files = {
 }
 
 
-def test_build_sdist(monkeypatch, tmpdir):
+def read_tz_file(tar: tarfile.TarFile, name: str) -> bytes:
+    start = tar.getnames()[0] + "/"
+    inner_file = tar.extractfile(tar.getmember(f"{start}{name}"))
+    assert inner_file
+    with contextlib.closing(inner_file) as f:
+        return f.read()
 
+
+def normalize_line_endings(value: bytes) -> bytes:
+    return value.replace(os.linesep.encode("utf-8"), b"\n")
+
+
+def test_build_sdist(monkeypatch, tmpdir):
     monkeypatch.chdir(MAIN_DIR)
 
-    out = subprocess.check_output(
-        [
-            sys.executable,
-            "-m",
-            "build",
-            "--sdist",
-            "--outdir",
-            str(tmpdir),
-        ]
+    subprocess.run(
+        [sys.executable, "-m", "build", "--sdist", f"--outdir={tmpdir}"], check=True
     )
-    if hasattr(out, "decode"):
-        out = out.decode()
 
     (sdist,) = tmpdir.visit("*.tar.gz")
 
@@ -125,25 +151,17 @@ def test_build_sdist(monkeypatch, tmpdir):
         version = start[9:-1]
         simpler = {n.split("/", 1)[-1] for n in tar.getnames()[1:]}
 
-        with contextlib.closing(
-            tar.extractfile(tar.getmember(start + "setup.py"))
-        ) as f:
-            setup_py = f.read()
+        setup_py = read_tz_file(tar, "setup.py")
+        pyproject_toml = read_tz_file(tar, "pyproject.toml")
+        pkgconfig = read_tz_file(tar, "pybind11/share/pkgconfig/pybind11.pc")
+        cmake_cfg = read_tz_file(
+            tar, "pybind11/share/cmake/pybind11/pybind11Config.cmake"
+        )
 
-        with contextlib.closing(
-            tar.extractfile(tar.getmember(start + "pyproject.toml"))
-        ) as f:
-            pyproject_toml = f.read()
-
-        with contextlib.closing(
-            tar.extractfile(
-                tar.getmember(
-                    start + "pybind11/share/cmake/pybind11/pybind11Config.cmake"
-                )
-            )
-        ) as f:
-            contents = f.read().decode("utf8")
-        assert 'set(pybind11_INCLUDE_DIR "${PACKAGE_PREFIX_DIR}/include")' in contents
+    assert (
+        'set(pybind11_INCLUDE_DIR "${PACKAGE_PREFIX_DIR}/include")'
+        in cmake_cfg.decode("utf-8")
+    )
 
     files = {f"pybind11/{n}" for n in all_files}
     files |= sdist_files
@@ -154,9 +172,9 @@ def test_build_sdist(monkeypatch, tmpdir):
 
     with open(os.path.join(MAIN_DIR, "tools", "setup_main.py.in"), "rb") as f:
         contents = (
-            string.Template(f.read().decode())
+            string.Template(f.read().decode("utf-8"))
             .substitute(version=version, extra_cmd="")
-            .encode()
+            .encode("utf-8")
         )
     assert setup_py == contents
 
@@ -164,25 +182,18 @@ def test_build_sdist(monkeypatch, tmpdir):
         contents = f.read()
     assert pyproject_toml == contents
 
+    simple_version = ".".join(version.split(".")[:3])
+    pkgconfig_expected = PKGCONFIG.format(VERSION=simple_version).encode("utf-8")
+    assert normalize_line_endings(pkgconfig) == pkgconfig_expected
+
 
 def test_build_global_dist(monkeypatch, tmpdir):
-
     monkeypatch.chdir(MAIN_DIR)
     monkeypatch.setenv("PYBIND11_GLOBAL_SDIST", "1")
-    out = subprocess.check_output(
-        [
-            sys.executable,
-            "-m",
-            "build",
-            "--sdist",
-            "--outdir",
-            str(tmpdir),
-        ]
+    subprocess.run(
+        [sys.executable, "-m", "build", "--sdist", "--outdir", str(tmpdir)], check=True
     )
 
-    if hasattr(out, "decode"):
-        out = out.decode()
-
     (sdist,) = tmpdir.visit("*.tar.gz")
 
     with tarfile.open(str(sdist), "r:gz") as tar:
@@ -190,15 +201,17 @@ def test_build_global_dist(monkeypatch, tmpdir):
         version = start[16:-1]
         simpler = {n.split("/", 1)[-1] for n in tar.getnames()[1:]}
 
-        with contextlib.closing(
-            tar.extractfile(tar.getmember(start + "setup.py"))
-        ) as f:
-            setup_py = f.read()
+        setup_py = read_tz_file(tar, "setup.py")
+        pyproject_toml = read_tz_file(tar, "pyproject.toml")
+        pkgconfig = read_tz_file(tar, "pybind11/share/pkgconfig/pybind11.pc")
+        cmake_cfg = read_tz_file(
+            tar, "pybind11/share/cmake/pybind11/pybind11Config.cmake"
+        )
 
-        with contextlib.closing(
-            tar.extractfile(tar.getmember(start + "pyproject.toml"))
-        ) as f:
-            pyproject_toml = f.read()
+    assert (
+        'set(pybind11_INCLUDE_DIR "${PACKAGE_PREFIX_DIR}/include")'
+        in cmake_cfg.decode("utf-8")
+    )
 
     files = {f"pybind11/{n}" for n in all_files}
     files |= sdist_files
@@ -209,7 +222,7 @@ def test_build_global_dist(monkeypatch, tmpdir):
         contents = (
             string.Template(f.read().decode())
             .substitute(version=version, extra_cmd="")
-            .encode()
+            .encode("utf-8")
         )
         assert setup_py == contents
 
@@ -217,12 +230,16 @@ def test_build_global_dist(monkeypatch, tmpdir):
         contents = f.read()
         assert pyproject_toml == contents
 
+    simple_version = ".".join(version.split(".")[:3])
+    pkgconfig_expected = PKGCONFIG.format(VERSION=simple_version).encode("utf-8")
+    assert normalize_line_endings(pkgconfig) == pkgconfig_expected
+
 
 def tests_build_wheel(monkeypatch, tmpdir):
     monkeypatch.chdir(MAIN_DIR)
 
-    subprocess.check_output(
-        [sys.executable, "-m", "pip", "wheel", ".", "-w", str(tmpdir)]
+    subprocess.run(
+        [sys.executable, "-m", "pip", "wheel", ".", "-w", str(tmpdir)], check=True
     )
 
     (wheel,) = tmpdir.visit("*.whl")
@@ -249,8 +266,8 @@ def tests_build_global_wheel(monkeypatch, tmpdir):
     monkeypatch.chdir(MAIN_DIR)
     monkeypatch.setenv("PYBIND11_GLOBAL_SDIST", "1")
 
-    subprocess.check_output(
-        [sys.executable, "-m", "pip", "wheel", ".", "-w", str(tmpdir)]
+    subprocess.run(
+        [sys.executable, "-m", "pip", "wheel", ".", "-w", str(tmpdir)], check=True
     )
 
     (wheel,) = tmpdir.visit("*.whl")
diff --git a/wrap/pybind11/tests/pybind11_tests.cpp b/wrap/pybind11/tests/pybind11_tests.cpp
index aa3095594..624034648 100644
--- a/wrap/pybind11/tests/pybind11_tests.cpp
+++ b/wrap/pybind11/tests/pybind11_tests.cpp
@@ -89,6 +89,12 @@ PYBIND11_MODULE(pybind11_tests, m) {
 #endif
     m.attr("cpp_std") = cpp_std();
     m.attr("PYBIND11_INTERNALS_ID") = PYBIND11_INTERNALS_ID;
+    m.attr("PYBIND11_SIMPLE_GIL_MANAGEMENT") =
+#if defined(PYBIND11_SIMPLE_GIL_MANAGEMENT)
+        true;
+#else
+        false;
+#endif
 
     bind_ConstructorStats(m);
 
diff --git a/wrap/pybind11/tests/requirements.txt b/wrap/pybind11/tests/requirements.txt
index 04aafa8cf..4ba101119 100644
--- a/wrap/pybind11/tests/requirements.txt
+++ b/wrap/pybind11/tests/requirements.txt
@@ -6,4 +6,4 @@ numpy==1.22.2; platform_python_implementation!="PyPy" and python_version>="3.10"
 pytest==7.0.0
 pytest-timeout
 scipy==1.5.4; platform_python_implementation!="PyPy" and python_version<"3.10"
-scipy==1.8.0; platform_python_implementation!="PyPy" and python_version=="3.10"
+scipy==1.10.0; platform_python_implementation!="PyPy" and python_version=="3.10"
diff --git a/wrap/pybind11/tests/test_async.py b/wrap/pybind11/tests/test_async.py
index b9ff9514d..83a4c5036 100644
--- a/wrap/pybind11/tests/test_async.py
+++ b/wrap/pybind11/tests/test_async.py
@@ -4,7 +4,7 @@ asyncio = pytest.importorskip("asyncio")
 m = pytest.importorskip("pybind11_tests.async_module")
 
 
-@pytest.fixture
+@pytest.fixture()
 def event_loop():
     loop = asyncio.new_event_loop()
     yield loop
@@ -16,7 +16,7 @@ async def get_await_result(x):
 
 
 def test_await(event_loop):
-    assert 5 == event_loop.run_until_complete(get_await_result(m.SupportsAsync()))
+    assert event_loop.run_until_complete(get_await_result(m.SupportsAsync())) == 5
 
 
 def test_await_missing(event_loop):
diff --git a/wrap/pybind11/tests/test_buffers.cpp b/wrap/pybind11/tests/test_buffers.cpp
index 6b6e8cba7..b5b8c355b 100644
--- a/wrap/pybind11/tests/test_buffers.cpp
+++ b/wrap/pybind11/tests/test_buffers.cpp
@@ -7,12 +7,47 @@
     BSD-style license that can be found in the LICENSE file.
 */
 
+#include <pybind11/complex.h>
 #include <pybind11/stl.h>
 
 #include "constructor_stats.h"
 #include "pybind11_tests.h"
 
 TEST_SUBMODULE(buffers, m) {
+    m.attr("long_double_and_double_have_same_size") = (sizeof(long double) == sizeof(double));
+
+    m.def("format_descriptor_format_buffer_info_equiv",
+          [](const std::string &cpp_name, const py::buffer &buffer) {
+              // https://google.github.io/styleguide/cppguide.html#Static_and_Global_Variables
+              static auto *format_table = new std::map<std::string, std::string>;
+              static auto *equiv_table
+                  = new std::map<std::string, bool (py::buffer_info::*)() const>;
+              if (format_table->empty()) {
+#define PYBIND11_ASSIGN_HELPER(...)                                                               \
+    (*format_table)[#__VA_ARGS__] = py::format_descriptor<__VA_ARGS__>::format();                 \
+    (*equiv_table)[#__VA_ARGS__] = &py::buffer_info::item_type_is_equivalent_to<__VA_ARGS__>;
+                  PYBIND11_ASSIGN_HELPER(PyObject *)
+                  PYBIND11_ASSIGN_HELPER(bool)
+                  PYBIND11_ASSIGN_HELPER(std::int8_t)
+                  PYBIND11_ASSIGN_HELPER(std::uint8_t)
+                  PYBIND11_ASSIGN_HELPER(std::int16_t)
+                  PYBIND11_ASSIGN_HELPER(std::uint16_t)
+                  PYBIND11_ASSIGN_HELPER(std::int32_t)
+                  PYBIND11_ASSIGN_HELPER(std::uint32_t)
+                  PYBIND11_ASSIGN_HELPER(std::int64_t)
+                  PYBIND11_ASSIGN_HELPER(std::uint64_t)
+                  PYBIND11_ASSIGN_HELPER(float)
+                  PYBIND11_ASSIGN_HELPER(double)
+                  PYBIND11_ASSIGN_HELPER(long double)
+                  PYBIND11_ASSIGN_HELPER(std::complex<float>)
+                  PYBIND11_ASSIGN_HELPER(std::complex<double>)
+                  PYBIND11_ASSIGN_HELPER(std::complex<long double>)
+#undef PYBIND11_ASSIGN_HELPER
+              }
+              return std::pair<std::string, bool>(
+                  (*format_table)[cpp_name], (buffer.request().*((*equiv_table)[cpp_name]))());
+          });
+
     // test_from_python / test_to_python:
     class Matrix {
     public:
diff --git a/wrap/pybind11/tests/test_buffers.py b/wrap/pybind11/tests/test_buffers.py
index 8354b68cd..63d9d869f 100644
--- a/wrap/pybind11/tests/test_buffers.py
+++ b/wrap/pybind11/tests/test_buffers.py
@@ -10,6 +10,63 @@ from pybind11_tests import buffers as m
 
 np = pytest.importorskip("numpy")
 
+if m.long_double_and_double_have_same_size:
+    # Determined by the compiler used to build the pybind11 tests
+    # (e.g. MSVC gets here, but MinGW might not).
+    np_float128 = None
+    np_complex256 = None
+else:
+    # Determined by the compiler used to build numpy (e.g. MinGW).
+    np_float128 = getattr(np, *["float128"] * 2)
+    np_complex256 = getattr(np, *["complex256"] * 2)
+
+CPP_NAME_FORMAT_NP_DTYPE_TABLE = [
+    ("PyObject *", "O", object),
+    ("bool", "?", np.bool_),
+    ("std::int8_t", "b", np.int8),
+    ("std::uint8_t", "B", np.uint8),
+    ("std::int16_t", "h", np.int16),
+    ("std::uint16_t", "H", np.uint16),
+    ("std::int32_t", "i", np.int32),
+    ("std::uint32_t", "I", np.uint32),
+    ("std::int64_t", "q", np.int64),
+    ("std::uint64_t", "Q", np.uint64),
+    ("float", "f", np.float32),
+    ("double", "d", np.float64),
+    ("long double", "g", np_float128),
+    ("std::complex<float>", "Zf", np.complex64),
+    ("std::complex<double>", "Zd", np.complex128),
+    ("std::complex<long double>", "Zg", np_complex256),
+]
+CPP_NAME_FORMAT_TABLE = [
+    (cpp_name, format)
+    for cpp_name, format, np_dtype in CPP_NAME_FORMAT_NP_DTYPE_TABLE
+    if np_dtype is not None
+]
+CPP_NAME_NP_DTYPE_TABLE = [
+    (cpp_name, np_dtype) for cpp_name, _, np_dtype in CPP_NAME_FORMAT_NP_DTYPE_TABLE
+]
+
+
+@pytest.mark.parametrize(("cpp_name", "np_dtype"), CPP_NAME_NP_DTYPE_TABLE)
+def test_format_descriptor_format_buffer_info_equiv(cpp_name, np_dtype):
+    if np_dtype is None:
+        pytest.skip(
+            f"cpp_name=`{cpp_name}`: `long double` and `double` have same size."
+        )
+    if isinstance(np_dtype, str):
+        pytest.skip(f"np.{np_dtype} does not exist.")
+    np_array = np.array([], dtype=np_dtype)
+    for other_cpp_name, expected_format in CPP_NAME_FORMAT_TABLE:
+        format, np_array_is_matching = m.format_descriptor_format_buffer_info_equiv(
+            other_cpp_name, np_array
+        )
+        assert format == expected_format
+        if other_cpp_name == cpp_name:
+            assert np_array_is_matching
+        else:
+            assert not np_array_is_matching
+
 
 def test_from_python():
     with pytest.raises(RuntimeError) as excinfo:
@@ -54,7 +111,8 @@ def test_to_python():
     mat2 = np.array(mat, copy=False)
     assert mat2.shape == (5, 4)
     assert abs(mat2).sum() == 11
-    assert mat2[2, 3] == 4 and mat2[3, 2] == 7
+    assert mat2[2, 3] == 4
+    assert mat2[3, 2] == 7
     mat2[2, 3] = 5
     assert mat2[2, 3] == 5
 
diff --git a/wrap/pybind11/tests/test_builtin_casters.cpp b/wrap/pybind11/tests/test_builtin_casters.cpp
index 6529f47d0..0623b85dc 100644
--- a/wrap/pybind11/tests/test_builtin_casters.cpp
+++ b/wrap/pybind11/tests/test_builtin_casters.cpp
@@ -73,6 +73,9 @@ PYBIND11_NAMESPACE_END(detail)
 PYBIND11_NAMESPACE_END(pybind11)
 
 TEST_SUBMODULE(builtin_casters, m) {
+    PYBIND11_WARNING_PUSH
+    PYBIND11_WARNING_DISABLE_MSVC(4127)
+
     // test_simple_string
     m.def("string_roundtrip", [](const char *s) { return s; });
 
@@ -86,7 +89,7 @@ TEST_SUBMODULE(builtin_casters, m) {
     std::wstring wstr;
     wstr.push_back(0x61);   // a
     wstr.push_back(0x2e18); // ⸘
-    if (PYBIND11_SILENCE_MSVC_C4127(sizeof(wchar_t) == 2)) {
+    if (sizeof(wchar_t) == 2) {
         wstr.push_back(mathbfA16_1);
         wstr.push_back(mathbfA16_2);
     } // 𝐀, utf16
@@ -113,7 +116,7 @@ TEST_SUBMODULE(builtin_casters, m) {
     // Under Python 2.7, invalid unicode UTF-32 characters didn't appear to trigger
     // UnicodeDecodeError
     m.def("bad_utf32_string", [=]() { return std::u32string({a32, char32_t(0xd800), z32}); });
-    if (PYBIND11_SILENCE_MSVC_C4127(sizeof(wchar_t) == 2)) {
+    if (sizeof(wchar_t) == 2) {
         m.def("bad_wchar_string", [=]() {
             return std::wstring({wchar_t(0x61), wchar_t(0xd800)});
         });
@@ -266,9 +269,14 @@ TEST_SUBMODULE(builtin_casters, m) {
     });
     m.def("lvalue_nested", []() -> const decltype(lvnested) & { return lvnested; });
 
-    static std::pair<int, std::string> int_string_pair{2, "items"};
     m.def(
-        "int_string_pair", []() { return &int_string_pair; }, py::return_value_policy::reference);
+        "int_string_pair",
+        []() {
+            // Using no-destructor idiom to side-step warnings from overzealous compilers.
+            static auto *int_string_pair = new std::pair<int, std::string>{2, "items"};
+            return int_string_pair;
+        },
+        py::return_value_policy::reference);
 
     // test_builtins_cast_return_none
     m.def("return_none_string", []() -> std::string * { return nullptr; });
@@ -379,4 +387,6 @@ TEST_SUBMODULE(builtin_casters, m) {
     m.def("takes_const_ref", [](const ConstRefCasted &x) { return x.tag; });
     m.def("takes_const_ref_wrap",
           [](std::reference_wrapper<const ConstRefCasted> x) { return x.get().tag; });
+
+    PYBIND11_WARNING_POP
 }
diff --git a/wrap/pybind11/tests/test_builtin_casters.py b/wrap/pybind11/tests/test_builtin_casters.py
index d38ae6802..b1f57bdd9 100644
--- a/wrap/pybind11/tests/test_builtin_casters.py
+++ b/wrap/pybind11/tests/test_builtin_casters.py
@@ -126,8 +126,8 @@ def test_bytes_to_string():
 
     assert m.strlen(b"hi") == 2
     assert m.string_length(b"world") == 5
-    assert m.string_length("a\x00b".encode()) == 3
-    assert m.strlen("a\x00b".encode()) == 1  # C-string limitation
+    assert m.string_length(b"a\x00b") == 3
+    assert m.strlen(b"a\x00b") == 1  # C-string limitation
 
     # passing in a utf8 encoded string should work
     assert m.string_length("💩".encode()) == 4
@@ -421,13 +421,15 @@ def test_reference_wrapper():
     a2 = m.refwrap_list(copy=True)
     assert [x.value for x in a1] == [2, 3]
     assert [x.value for x in a2] == [2, 3]
-    assert not a1[0] is a2[0] and not a1[1] is a2[1]
+    assert a1[0] is not a2[0]
+    assert a1[1] is not a2[1]
 
     b1 = m.refwrap_list(copy=False)
     b2 = m.refwrap_list(copy=False)
     assert [x.value for x in b1] == [1, 2]
     assert [x.value for x in b2] == [1, 2]
-    assert b1[0] is b2[0] and b1[1] is b2[1]
+    assert b1[0] is b2[0]
+    assert b1[1] is b2[1]
 
     assert m.refwrap_iiw(IncType(5)) == 5
     assert m.refwrap_call_iiw(IncType(10), m.refwrap_iiw) == [10, 10, 10, 10]
diff --git a/wrap/pybind11/tests/test_callbacks.cpp b/wrap/pybind11/tests/test_callbacks.cpp
index 92b8053de..2fd05dec7 100644
--- a/wrap/pybind11/tests/test_callbacks.cpp
+++ b/wrap/pybind11/tests/test_callbacks.cpp
@@ -240,4 +240,41 @@ TEST_SUBMODULE(callbacks, m) {
             f();
         }
     });
+
+    auto *custom_def = []() {
+        static PyMethodDef def;
+        def.ml_name = "example_name";
+        def.ml_doc = "Example doc";
+        def.ml_meth = [](PyObject *, PyObject *args) -> PyObject * {
+            if (PyTuple_Size(args) != 1) {
+                throw std::runtime_error("Invalid number of arguments for example_name");
+            }
+            PyObject *first = PyTuple_GetItem(args, 0);
+            if (!PyLong_Check(first)) {
+                throw std::runtime_error("Invalid argument to example_name");
+            }
+            auto result = py::cast(PyLong_AsLong(first) * 9);
+            return result.release().ptr();
+        };
+        def.ml_flags = METH_VARARGS;
+        return &def;
+    }();
+
+    // rec_capsule with name that has the same value (but not pointer) as our internal one
+    // This capsule should be detected by our code as foreign and not inspected as the pointers
+    // shouldn't match
+    constexpr const char *rec_capsule_name
+        = pybind11::detail::internals_function_record_capsule_name;
+    py::capsule rec_capsule(std::malloc(1), [](void *data) { std::free(data); });
+    rec_capsule.set_name(rec_capsule_name);
+    m.add_object("custom_function", PyCFunction_New(custom_def, rec_capsule.ptr()));
+
+    // This test requires a new ABI version to pass
+#if PYBIND11_INTERNALS_VERSION > 4
+    // rec_capsule with nullptr name
+    py::capsule rec_capsule2(std::malloc(1), [](void *data) { std::free(data); });
+    m.add_object("custom_function2", PyCFunction_New(custom_def, rec_capsule2.ptr()));
+#else
+    m.add_object("custom_function2", py::none());
+#endif
 }
diff --git a/wrap/pybind11/tests/test_callbacks.py b/wrap/pybind11/tests/test_callbacks.py
index 0b1047bbf..4a652f53e 100644
--- a/wrap/pybind11/tests/test_callbacks.py
+++ b/wrap/pybind11/tests/test_callbacks.py
@@ -5,6 +5,7 @@ import pytest
 
 import env  # noqa: F401
 from pybind11_tests import callbacks as m
+from pybind11_tests import detailed_error_messages_enabled
 
 
 def test_callbacks():
@@ -70,11 +71,20 @@ def test_keyword_args_and_generalized_unpacking():
 
     with pytest.raises(RuntimeError) as excinfo:
         m.test_arg_conversion_error1(f)
-    assert "Unable to convert call argument" in str(excinfo.value)
+    assert str(excinfo.value) == "Unable to convert call argument " + (
+        "'1' of type 'UnregisteredType' to Python object"
+        if detailed_error_messages_enabled
+        else "'1' to Python object (#define PYBIND11_DETAILED_ERROR_MESSAGES or compile in debug mode for details)"
+    )
 
     with pytest.raises(RuntimeError) as excinfo:
         m.test_arg_conversion_error2(f)
-    assert "Unable to convert call argument" in str(excinfo.value)
+    assert str(excinfo.value) == "Unable to convert call argument " + (
+        "'expected_name' of type 'UnregisteredType' to Python object"
+        if detailed_error_messages_enabled
+        else "'expected_name' to Python object "
+        "(#define PYBIND11_DETAILED_ERROR_MESSAGES or compile in debug mode for details)"
+    )
 
 
 def test_lambda_closure_cleanup():
@@ -193,3 +203,16 @@ def test_callback_num_times():
     if len(rates) > 1:
         print("Min    Mean   Max")
         print(f"{min(rates):6.3f} {sum(rates) / len(rates):6.3f} {max(rates):6.3f}")
+
+
+def test_custom_func():
+    assert m.custom_function(4) == 36
+    assert m.roundtrip(m.custom_function)(4) == 36
+
+
+@pytest.mark.skipif(
+    m.custom_function2 is None, reason="Current PYBIND11_INTERNALS_VERSION too low"
+)
+def test_custom_func2():
+    assert m.custom_function2(3) == 27
+    assert m.roundtrip(m.custom_function2)(3) == 27
diff --git a/wrap/pybind11/tests/test_chrono.py b/wrap/pybind11/tests/test_chrono.py
index 7f47b37a2..a29316c38 100644
--- a/wrap/pybind11/tests/test_chrono.py
+++ b/wrap/pybind11/tests/test_chrono.py
@@ -7,7 +7,6 @@ from pybind11_tests import chrono as m
 
 
 def test_chrono_system_clock():
-
     # Get the time from both c++ and datetime
     date0 = datetime.datetime.today()
     date1 = m.test_chrono1()
@@ -122,7 +121,6 @@ def test_chrono_system_clock_roundtrip_time(time1, tz, monkeypatch):
 
 
 def test_chrono_duration_roundtrip():
-
     # Get the difference between two times (a timedelta)
     date1 = datetime.datetime.today()
     date2 = datetime.datetime.today()
@@ -143,7 +141,6 @@ def test_chrono_duration_roundtrip():
 
 
 def test_chrono_duration_subtraction_equivalence():
-
     date1 = datetime.datetime.today()
     date2 = datetime.datetime.today()
 
@@ -154,7 +151,6 @@ def test_chrono_duration_subtraction_equivalence():
 
 
 def test_chrono_duration_subtraction_equivalence_date():
-
     date1 = datetime.date.today()
     date2 = datetime.date.today()
 
diff --git a/wrap/pybind11/tests/test_class.cpp b/wrap/pybind11/tests/test_class.cpp
index c8b8071dc..7241bc881 100644
--- a/wrap/pybind11/tests/test_class.cpp
+++ b/wrap/pybind11/tests/test_class.cpp
@@ -22,10 +22,8 @@
 
 #include <utility>
 
-#if defined(_MSC_VER)
-#    pragma warning(disable : 4324)
+PYBIND11_WARNING_DISABLE_MSVC(4324)
 //     warning C4324: structure was padded due to alignment specifier
-#endif
 
 // test_brace_initialization
 struct NoBraceInitialization {
@@ -36,7 +34,29 @@ struct NoBraceInitialization {
     std::vector<int> vec;
 };
 
+namespace test_class {
+namespace pr4220_tripped_over_this { // PR #4227
+
+template <int>
+struct SoEmpty {};
+
+template <typename T>
+std::string get_msg(const T &) {
+    return "This is really only meant to exercise successful compilation.";
+}
+
+using Empty0 = SoEmpty<0x0>;
+
+void bind_empty0(py::module_ &m) {
+    py::class_<Empty0>(m, "Empty0").def(py::init<>()).def("get_msg", get_msg<Empty0>);
+}
+
+} // namespace pr4220_tripped_over_this
+} // namespace test_class
+
 TEST_SUBMODULE(class_, m) {
+    m.def("obj_class_name", [](py::handle obj) { return py::detail::obj_class_name(obj.ptr()); });
+
     // test_instance
     struct NoConstructor {
         NoConstructor() = default;
@@ -65,7 +85,7 @@ TEST_SUBMODULE(class_, m) {
         .def_static("new_instance", &NoConstructor::new_instance, "Return an instance");
 
     py::class_<NoConstructorNew>(m, "NoConstructorNew")
-        .def(py::init([](const NoConstructorNew &self) { return self; })) // Need a NOOP __init__
+        .def(py::init([]() { return nullptr; })) // Need a NOOP __init__
         .def_static("__new__",
                     [](const py::object &) { return NoConstructorNew::new_instance(); });
 
@@ -364,6 +384,8 @@ TEST_SUBMODULE(class_, m) {
 
     protected:
         virtual int foo() const { return value; }
+        virtual void *void_foo() { return static_cast<void *>(&value); }
+        virtual void *get_self() { return static_cast<void *>(this); }
 
     private:
         int value = 42;
@@ -372,6 +394,8 @@ TEST_SUBMODULE(class_, m) {
     class TrampolineB : public ProtectedB {
     public:
         int foo() const override { PYBIND11_OVERRIDE(int, ProtectedB, foo, ); }
+        void *void_foo() override { PYBIND11_OVERRIDE(void *, ProtectedB, void_foo, ); }
+        void *get_self() override { PYBIND11_OVERRIDE(void *, ProtectedB, get_self, ); }
     };
 
     class PublicistB : public ProtectedB {
@@ -381,11 +405,23 @@ TEST_SUBMODULE(class_, m) {
         // (in Debug builds only, tested with icpc (ICC) 2021.1 Beta 20200827)
         ~PublicistB() override{}; // NOLINT(modernize-use-equals-default)
         using ProtectedB::foo;
+        using ProtectedB::get_self;
+        using ProtectedB::void_foo;
     };
 
+    m.def("read_foo", [](const void *original) {
+        const int *ptr = reinterpret_cast<const int *>(original);
+        return *ptr;
+    });
+
+    m.def("pointers_equal",
+          [](const void *original, const void *comparison) { return original == comparison; });
+
     py::class_<ProtectedB, TrampolineB>(m, "ProtectedB")
         .def(py::init<>())
-        .def("foo", &PublicistB::foo);
+        .def("foo", &PublicistB::foo)
+        .def("void_foo", &PublicistB::void_foo)
+        .def("get_self", &PublicistB::get_self);
 
     // test_brace_initialization
     struct BraceInitialization {
@@ -517,6 +553,8 @@ TEST_SUBMODULE(class_, m) {
         py::class_<OtherDuplicateNested>(gt, "OtherDuplicateNested");
         py::class_<OtherDuplicateNested>(gt, "YetAnotherDuplicateNested");
     });
+
+    test_class::pr4220_tripped_over_this::bind_empty0(m);
 }
 
 template <int N>
diff --git a/wrap/pybind11/tests/test_class.py b/wrap/pybind11/tests/test_class.py
index ff9196f0f..ee7467cf8 100644
--- a/wrap/pybind11/tests/test_class.py
+++ b/wrap/pybind11/tests/test_class.py
@@ -1,10 +1,16 @@
 import pytest
 
-import env  # noqa: F401
+import env
 from pybind11_tests import ConstructorStats, UserType
 from pybind11_tests import class_ as m
 
 
+def test_obj_class_name():
+    expected_name = "UserType" if env.PYPY else "pybind11_tests.UserType"
+    assert m.obj_class_name(UserType(1)) == expected_name
+    assert m.obj_class_name(UserType) == expected_name
+
+
 def test_repr():
     assert "pybind11_type" in repr(type(UserType))
     assert "UserType" in repr(UserType)
@@ -23,7 +29,7 @@ def test_instance(msg):
     assert cstats.alive() == 0
 
 
-def test_instance_new(msg):
+def test_instance_new():
     instance = m.NoConstructorNew()  # .__new__(m.NoConstructor.__class__)
     cstats = ConstructorStats.get(m.NoConstructorNew)
     assert cstats.alive() == 1
@@ -176,7 +182,6 @@ def test_inheritance(msg):
 
 
 def test_inheritance_init(msg):
-
     # Single base
     class Python(m.Pet):
         def __init__(self):
@@ -213,7 +218,7 @@ def test_automatic_upcasting():
 
 
 def test_isinstance():
-    objects = [tuple(), dict(), m.Pet("Polly", "parrot")] + [m.Dog("Molly")] * 4
+    objects = [(), {}, m.Pet("Polly", "parrot")] + [m.Dog("Molly")] * 4
     expected = (True, True, True, True, True, False, False)
     assert m.check_instances(objects) == expected
 
@@ -313,6 +318,8 @@ def test_bind_protected_functions():
 
     b = m.ProtectedB()
     assert b.foo() == 42
+    assert m.read_foo(b.void_foo()) == 42
+    assert m.pointers_equal(b.get_self(), b)
 
     class C(m.ProtectedB):
         def __init__(self):
@@ -417,7 +424,7 @@ def test_exception_rvalue_abort():
 
 
 # https://github.com/pybind/pybind11/issues/1568
-def test_multiple_instances_with_same_pointer(capture):
+def test_multiple_instances_with_same_pointer():
     n = 100
     instances = [m.SamePointer() for _ in range(n)]
     for i in range(n):
@@ -469,3 +476,10 @@ def test_register_duplicate_class():
         m.register_duplicate_nested_class_type(ClassScope)
     expected = 'generic_type: type "YetAnotherDuplicateNested" is already registered!'
     assert str(exc_info.value) == expected
+
+
+def test_pr4220_tripped_over_this():
+    assert (
+        m.Empty0().get_msg()
+        == "This is really only meant to exercise successful compilation."
+    )
diff --git a/wrap/pybind11/tests/test_cmake_build/CMakeLists.txt b/wrap/pybind11/tests/test_cmake_build/CMakeLists.txt
index 8bfaa386a..e5aa975cf 100644
--- a/wrap/pybind11/tests/test_cmake_build/CMakeLists.txt
+++ b/wrap/pybind11/tests/test_cmake_build/CMakeLists.txt
@@ -1,6 +1,3 @@
-# Built-in in CMake 3.5+
-include(CMakeParseArguments)
-
 add_custom_target(test_cmake_build)
 
 function(pybind11_add_build_test name)
diff --git a/wrap/pybind11/tests/test_cmake_build/installed_embed/CMakeLists.txt b/wrap/pybind11/tests/test_cmake_build/installed_embed/CMakeLists.txt
index f7d693998..d9dcb45e4 100644
--- a/wrap/pybind11/tests/test_cmake_build/installed_embed/CMakeLists.txt
+++ b/wrap/pybind11/tests/test_cmake_build/installed_embed/CMakeLists.txt
@@ -1,12 +1,12 @@
-cmake_minimum_required(VERSION 3.4)
+cmake_minimum_required(VERSION 3.5)
 
-# The `cmake_minimum_required(VERSION 3.4...3.18)` syntax does not work with
+# The `cmake_minimum_required(VERSION 3.5...3.26)` syntax does not work with
 # some versions of VS that have a patched CMake 3.11. This forces us to emulate
 # the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.18)
+if(${CMAKE_VERSION} VERSION_LESS 3.26)
   cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
-  cmake_policy(VERSION 3.18)
+  cmake_policy(VERSION 3.26)
 endif()
 
 project(test_installed_embed CXX)
diff --git a/wrap/pybind11/tests/test_cmake_build/installed_function/CMakeLists.txt b/wrap/pybind11/tests/test_cmake_build/installed_function/CMakeLists.txt
index d7ca4db55..2f4f64275 100644
--- a/wrap/pybind11/tests/test_cmake_build/installed_function/CMakeLists.txt
+++ b/wrap/pybind11/tests/test_cmake_build/installed_function/CMakeLists.txt
@@ -1,13 +1,13 @@
-cmake_minimum_required(VERSION 3.4)
+cmake_minimum_required(VERSION 3.5)
 project(test_installed_module CXX)
 
-# The `cmake_minimum_required(VERSION 3.4...3.18)` syntax does not work with
+# The `cmake_minimum_required(VERSION 3.5...3.26)` syntax does not work with
 # some versions of VS that have a patched CMake 3.11. This forces us to emulate
 # the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.18)
+if(${CMAKE_VERSION} VERSION_LESS 3.26)
   cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
-  cmake_policy(VERSION 3.18)
+  cmake_policy(VERSION 3.26)
 endif()
 
 project(test_installed_function CXX)
diff --git a/wrap/pybind11/tests/test_cmake_build/installed_target/CMakeLists.txt b/wrap/pybind11/tests/test_cmake_build/installed_target/CMakeLists.txt
index bc5e101f1..a981e236f 100644
--- a/wrap/pybind11/tests/test_cmake_build/installed_target/CMakeLists.txt
+++ b/wrap/pybind11/tests/test_cmake_build/installed_target/CMakeLists.txt
@@ -1,12 +1,12 @@
-cmake_minimum_required(VERSION 3.4)
+cmake_minimum_required(VERSION 3.5)
 
-# The `cmake_minimum_required(VERSION 3.4...3.18)` syntax does not work with
+# The `cmake_minimum_required(VERSION 3.5...3.26)` syntax does not work with
 # some versions of VS that have a patched CMake 3.11. This forces us to emulate
 # the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.18)
+if(${CMAKE_VERSION} VERSION_LESS 3.26)
   cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
-  cmake_policy(VERSION 3.18)
+  cmake_policy(VERSION 3.26)
 endif()
 
 project(test_installed_target CXX)
diff --git a/wrap/pybind11/tests/test_cmake_build/subdirectory_embed/CMakeLists.txt b/wrap/pybind11/tests/test_cmake_build/subdirectory_embed/CMakeLists.txt
index 58cdd7cfd..f286746b9 100644
--- a/wrap/pybind11/tests/test_cmake_build/subdirectory_embed/CMakeLists.txt
+++ b/wrap/pybind11/tests/test_cmake_build/subdirectory_embed/CMakeLists.txt
@@ -1,12 +1,12 @@
-cmake_minimum_required(VERSION 3.4)
+cmake_minimum_required(VERSION 3.5)
 
-# The `cmake_minimum_required(VERSION 3.4...3.18)` syntax does not work with
+# The `cmake_minimum_required(VERSION 3.5...3.26)` syntax does not work with
 # some versions of VS that have a patched CMake 3.11. This forces us to emulate
 # the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.18)
+if(${CMAKE_VERSION} VERSION_LESS 3.26)
   cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
-  cmake_policy(VERSION 3.18)
+  cmake_policy(VERSION 3.26)
 endif()
 
 project(test_subdirectory_embed CXX)
diff --git a/wrap/pybind11/tests/test_cmake_build/subdirectory_function/CMakeLists.txt b/wrap/pybind11/tests/test_cmake_build/subdirectory_function/CMakeLists.txt
index 01557c439..275a75c0b 100644
--- a/wrap/pybind11/tests/test_cmake_build/subdirectory_function/CMakeLists.txt
+++ b/wrap/pybind11/tests/test_cmake_build/subdirectory_function/CMakeLists.txt
@@ -1,12 +1,12 @@
-cmake_minimum_required(VERSION 3.4)
+cmake_minimum_required(VERSION 3.5)
 
-# The `cmake_minimum_required(VERSION 3.4...3.18)` syntax does not work with
+# The `cmake_minimum_required(VERSION 3.5...3.26)` syntax does not work with
 # some versions of VS that have a patched CMake 3.11. This forces us to emulate
 # the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.18)
+if(${CMAKE_VERSION} VERSION_LESS 3.26)
   cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
-  cmake_policy(VERSION 3.18)
+  cmake_policy(VERSION 3.26)
 endif()
 
 project(test_subdirectory_function CXX)
diff --git a/wrap/pybind11/tests/test_cmake_build/subdirectory_target/CMakeLists.txt b/wrap/pybind11/tests/test_cmake_build/subdirectory_target/CMakeLists.txt
index ba82fdee2..37bb2c56e 100644
--- a/wrap/pybind11/tests/test_cmake_build/subdirectory_target/CMakeLists.txt
+++ b/wrap/pybind11/tests/test_cmake_build/subdirectory_target/CMakeLists.txt
@@ -1,12 +1,12 @@
-cmake_minimum_required(VERSION 3.4)
+cmake_minimum_required(VERSION 3.5)
 
-# The `cmake_minimum_required(VERSION 3.4...3.18)` syntax does not work with
+# The `cmake_minimum_required(VERSION 3.5...3.26)` syntax does not work with
 # some versions of VS that have a patched CMake 3.11. This forces us to emulate
 # the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.18)
+if(${CMAKE_VERSION} VERSION_LESS 3.26)
   cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
-  cmake_policy(VERSION 3.18)
+  cmake_policy(VERSION 3.26)
 endif()
 
 project(test_subdirectory_target CXX)
diff --git a/wrap/pybind11/tests/test_const_name.py b/wrap/pybind11/tests/test_const_name.py
index 10b0caee2..a145f0bbb 100644
--- a/wrap/pybind11/tests/test_const_name.py
+++ b/wrap/pybind11/tests/test_const_name.py
@@ -3,9 +3,9 @@ import pytest
 from pybind11_tests import const_name as m
 
 
-@pytest.mark.parametrize("func", (m.const_name_tests, m.underscore_tests))
+@pytest.mark.parametrize("func", [m.const_name_tests, m.underscore_tests])
 @pytest.mark.parametrize(
-    "selector, expected",
+    ("selector", "expected"),
     enumerate(
         (
             "",
diff --git a/wrap/pybind11/tests/test_constants_and_functions.cpp b/wrap/pybind11/tests/test_constants_and_functions.cpp
index 1918a429c..312edca9e 100644
--- a/wrap/pybind11/tests/test_constants_and_functions.cpp
+++ b/wrap/pybind11/tests/test_constants_and_functions.cpp
@@ -52,15 +52,12 @@ int f1(int x) noexcept { return x + 1; }
 #endif
 int f2(int x) noexcept(true) { return x + 2; }
 int f3(int x) noexcept(false) { return x + 3; }
-#if defined(__GNUG__) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic push
-#    pragma GCC diagnostic ignored "-Wdeprecated"
-#endif
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_GCC("-Wdeprecated")
+PYBIND11_WARNING_DISABLE_CLANG("-Wdeprecated")
 // NOLINTNEXTLINE(modernize-use-noexcept)
 int f4(int x) throw() { return x + 4; } // Deprecated equivalent to noexcept(true)
-#if defined(__GNUG__) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic pop
-#endif
+PYBIND11_WARNING_POP
 struct C {
     int m1(int x) noexcept { return x - 1; }
     int m2(int x) const noexcept { return x - 2; }
@@ -68,17 +65,14 @@ struct C {
     int m4(int x) const noexcept(true) { return x - 4; }
     int m5(int x) noexcept(false) { return x - 5; }
     int m6(int x) const noexcept(false) { return x - 6; }
-#if defined(__GNUG__) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic push
-#    pragma GCC diagnostic ignored "-Wdeprecated"
-#endif
+    PYBIND11_WARNING_PUSH
+    PYBIND11_WARNING_DISABLE_GCC("-Wdeprecated")
+    PYBIND11_WARNING_DISABLE_CLANG("-Wdeprecated")
     // NOLINTNEXTLINE(modernize-use-noexcept)
     int m7(int x) throw() { return x - 7; }
     // NOLINTNEXTLINE(modernize-use-noexcept)
     int m8(int x) const throw() { return x - 8; }
-#if defined(__GNUG__) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic pop
-#endif
+    PYBIND11_WARNING_POP
 };
 } // namespace test_exc_sp
 
@@ -126,14 +120,12 @@ TEST_SUBMODULE(constants_and_functions, m) {
         .def("m8", &C::m8);
     m.def("f1", f1);
     m.def("f2", f2);
-#if defined(__INTEL_COMPILER)
-#    pragma warning push
-#    pragma warning disable 878 // incompatible exception specifications
-#endif
+
+    PYBIND11_WARNING_PUSH
+    PYBIND11_WARNING_DISABLE_INTEL(878) // incompatible exception specifications
     m.def("f3", f3);
-#if defined(__INTEL_COMPILER)
-#    pragma warning pop
-#endif
+    PYBIND11_WARNING_POP
+
     m.def("f4", f4);
 
     // test_function_record_leaks
@@ -156,4 +148,7 @@ TEST_SUBMODULE(constants_and_functions, m) {
             py::arg_v("y", 42, "<the answer>"),
             py::arg_v("z", default_value));
     });
+
+    // test noexcept(true) lambda (#4565)
+    m.def("l1", []() noexcept(true) { return 0; });
 }
diff --git a/wrap/pybind11/tests/test_constants_and_functions.py b/wrap/pybind11/tests/test_constants_and_functions.py
index 5da0b84b8..a1142461c 100644
--- a/wrap/pybind11/tests/test_constants_and_functions.py
+++ b/wrap/pybind11/tests/test_constants_and_functions.py
@@ -50,3 +50,7 @@ def test_function_record_leaks():
         m.register_large_capture_with_invalid_arguments(m)
     with pytest.raises(RuntimeError):
         m.register_with_raising_repr(m, RaisingRepr())
+
+
+def test_noexcept_lambda():
+    assert m.l1() == 0
diff --git a/wrap/pybind11/tests/test_copy_move.cpp b/wrap/pybind11/tests/test_copy_move.cpp
index 28c244564..f54733550 100644
--- a/wrap/pybind11/tests/test_copy_move.cpp
+++ b/wrap/pybind11/tests/test_copy_move.cpp
@@ -13,6 +13,8 @@
 #include "constructor_stats.h"
 #include "pybind11_tests.h"
 
+#include <type_traits>
+
 template <typename derived>
 struct empty {
     static const derived &get_one() { return instance_; }
@@ -293,3 +295,239 @@ TEST_SUBMODULE(copy_move_policies, m) {
     // Make sure that cast from pytype rvalue to other pytype works
     m.def("get_pytype_rvalue_castissue", [](double i) { return py::float_(i).cast<py::int_>(); });
 }
+
+/*
+ * Rest of the file:
+ * static_assert based tests for pybind11 adaptations of
+ * std::is_move_constructible, std::is_copy_constructible and
+ * std::is_copy_assignable (no adaptation of std::is_move_assignable).
+ * Difference between pybind11 and std traits: pybind11 traits will also check
+ * the contained value_types.
+ */
+
+struct NotMovable {
+    NotMovable() = default;
+    NotMovable(NotMovable const &) = default;
+    NotMovable(NotMovable &&) = delete;
+    NotMovable &operator=(NotMovable const &) = default;
+    NotMovable &operator=(NotMovable &&) = delete;
+};
+static_assert(!std::is_move_constructible<NotMovable>::value,
+              "!std::is_move_constructible<NotMovable>::value");
+static_assert(std::is_copy_constructible<NotMovable>::value,
+              "std::is_copy_constructible<NotMovable>::value");
+static_assert(!pybind11::detail::is_move_constructible<NotMovable>::value,
+              "!pybind11::detail::is_move_constructible<NotMovable>::value");
+static_assert(pybind11::detail::is_copy_constructible<NotMovable>::value,
+              "pybind11::detail::is_copy_constructible<NotMovable>::value");
+static_assert(!std::is_move_assignable<NotMovable>::value,
+              "!std::is_move_assignable<NotMovable>::value");
+static_assert(std::is_copy_assignable<NotMovable>::value,
+              "std::is_copy_assignable<NotMovable>::value");
+// pybind11 does not have this
+// static_assert(!pybind11::detail::is_move_assignable<NotMovable>::value,
+//               "!pybind11::detail::is_move_assignable<NotMovable>::value");
+static_assert(pybind11::detail::is_copy_assignable<NotMovable>::value,
+              "pybind11::detail::is_copy_assignable<NotMovable>::value");
+
+struct NotCopyable {
+    NotCopyable() = default;
+    NotCopyable(NotCopyable const &) = delete;
+    NotCopyable(NotCopyable &&) = default;
+    NotCopyable &operator=(NotCopyable const &) = delete;
+    NotCopyable &operator=(NotCopyable &&) = default;
+};
+static_assert(std::is_move_constructible<NotCopyable>::value,
+              "std::is_move_constructible<NotCopyable>::value");
+static_assert(!std::is_copy_constructible<NotCopyable>::value,
+              "!std::is_copy_constructible<NotCopyable>::value");
+static_assert(pybind11::detail::is_move_constructible<NotCopyable>::value,
+              "pybind11::detail::is_move_constructible<NotCopyable>::value");
+static_assert(!pybind11::detail::is_copy_constructible<NotCopyable>::value,
+              "!pybind11::detail::is_copy_constructible<NotCopyable>::value");
+static_assert(std::is_move_assignable<NotCopyable>::value,
+              "std::is_move_assignable<NotCopyable>::value");
+static_assert(!std::is_copy_assignable<NotCopyable>::value,
+              "!std::is_copy_assignable<NotCopyable>::value");
+// pybind11 does not have this
+// static_assert(!pybind11::detail::is_move_assignable<NotCopyable>::value,
+//               "!pybind11::detail::is_move_assignable<NotCopyable>::value");
+static_assert(!pybind11::detail::is_copy_assignable<NotCopyable>::value,
+              "!pybind11::detail::is_copy_assignable<NotCopyable>::value");
+
+struct NotCopyableNotMovable {
+    NotCopyableNotMovable() = default;
+    NotCopyableNotMovable(NotCopyableNotMovable const &) = delete;
+    NotCopyableNotMovable(NotCopyableNotMovable &&) = delete;
+    NotCopyableNotMovable &operator=(NotCopyableNotMovable const &) = delete;
+    NotCopyableNotMovable &operator=(NotCopyableNotMovable &&) = delete;
+};
+static_assert(!std::is_move_constructible<NotCopyableNotMovable>::value,
+              "!std::is_move_constructible<NotCopyableNotMovable>::value");
+static_assert(!std::is_copy_constructible<NotCopyableNotMovable>::value,
+              "!std::is_copy_constructible<NotCopyableNotMovable>::value");
+static_assert(!pybind11::detail::is_move_constructible<NotCopyableNotMovable>::value,
+              "!pybind11::detail::is_move_constructible<NotCopyableNotMovable>::value");
+static_assert(!pybind11::detail::is_copy_constructible<NotCopyableNotMovable>::value,
+              "!pybind11::detail::is_copy_constructible<NotCopyableNotMovable>::value");
+static_assert(!std::is_move_assignable<NotCopyableNotMovable>::value,
+              "!std::is_move_assignable<NotCopyableNotMovable>::value");
+static_assert(!std::is_copy_assignable<NotCopyableNotMovable>::value,
+              "!std::is_copy_assignable<NotCopyableNotMovable>::value");
+// pybind11 does not have this
+// static_assert(!pybind11::detail::is_move_assignable<NotCopyableNotMovable>::value,
+//               "!pybind11::detail::is_move_assignable<NotCopyableNotMovable>::value");
+static_assert(!pybind11::detail::is_copy_assignable<NotCopyableNotMovable>::value,
+              "!pybind11::detail::is_copy_assignable<NotCopyableNotMovable>::value");
+
+struct NotMovableVector : std::vector<NotMovable> {};
+static_assert(std::is_move_constructible<NotMovableVector>::value,
+              "std::is_move_constructible<NotMovableVector>::value");
+static_assert(std::is_copy_constructible<NotMovableVector>::value,
+              "std::is_copy_constructible<NotMovableVector>::value");
+static_assert(!pybind11::detail::is_move_constructible<NotMovableVector>::value,
+              "!pybind11::detail::is_move_constructible<NotMovableVector>::value");
+static_assert(pybind11::detail::is_copy_constructible<NotMovableVector>::value,
+              "pybind11::detail::is_copy_constructible<NotMovableVector>::value");
+static_assert(std::is_move_assignable<NotMovableVector>::value,
+              "std::is_move_assignable<NotMovableVector>::value");
+static_assert(std::is_copy_assignable<NotMovableVector>::value,
+              "std::is_copy_assignable<NotMovableVector>::value");
+// pybind11 does not have this
+// static_assert(!pybind11::detail::is_move_assignable<NotMovableVector>::value,
+//               "!pybind11::detail::is_move_assignable<NotMovableVector>::value");
+static_assert(pybind11::detail::is_copy_assignable<NotMovableVector>::value,
+              "pybind11::detail::is_copy_assignable<NotMovableVector>::value");
+
+struct NotCopyableVector : std::vector<NotCopyable> {};
+static_assert(std::is_move_constructible<NotCopyableVector>::value,
+              "std::is_move_constructible<NotCopyableVector>::value");
+static_assert(std::is_copy_constructible<NotCopyableVector>::value,
+              "std::is_copy_constructible<NotCopyableVector>::value");
+static_assert(pybind11::detail::is_move_constructible<NotCopyableVector>::value,
+              "pybind11::detail::is_move_constructible<NotCopyableVector>::value");
+static_assert(!pybind11::detail::is_copy_constructible<NotCopyableVector>::value,
+              "!pybind11::detail::is_copy_constructible<NotCopyableVector>::value");
+static_assert(std::is_move_assignable<NotCopyableVector>::value,
+              "std::is_move_assignable<NotCopyableVector>::value");
+static_assert(std::is_copy_assignable<NotCopyableVector>::value,
+              "std::is_copy_assignable<NotCopyableVector>::value");
+// pybind11 does not have this
+// static_assert(!pybind11::detail::is_move_assignable<NotCopyableVector>::value,
+//               "!pybind11::detail::is_move_assignable<NotCopyableVector>::value");
+static_assert(!pybind11::detail::is_copy_assignable<NotCopyableVector>::value,
+              "!pybind11::detail::is_copy_assignable<NotCopyableVector>::value");
+
+struct NotCopyableNotMovableVector : std::vector<NotCopyableNotMovable> {};
+static_assert(std::is_move_constructible<NotCopyableNotMovableVector>::value,
+              "std::is_move_constructible<NotCopyableNotMovableVector>::value");
+static_assert(std::is_copy_constructible<NotCopyableNotMovableVector>::value,
+              "std::is_copy_constructible<NotCopyableNotMovableVector>::value");
+static_assert(!pybind11::detail::is_move_constructible<NotCopyableNotMovableVector>::value,
+              "!pybind11::detail::is_move_constructible<NotCopyableNotMovableVector>::value");
+static_assert(!pybind11::detail::is_copy_constructible<NotCopyableNotMovableVector>::value,
+              "!pybind11::detail::is_copy_constructible<NotCopyableNotMovableVector>::value");
+static_assert(std::is_move_assignable<NotCopyableNotMovableVector>::value,
+              "std::is_move_assignable<NotCopyableNotMovableVector>::value");
+static_assert(std::is_copy_assignable<NotCopyableNotMovableVector>::value,
+              "std::is_copy_assignable<NotCopyableNotMovableVector>::value");
+// pybind11 does not have this
+// static_assert(!pybind11::detail::is_move_assignable<NotCopyableNotMovableVector>::value,
+//               "!pybind11::detail::is_move_assignable<NotCopyableNotMovableVector>::value");
+static_assert(!pybind11::detail::is_copy_assignable<NotCopyableNotMovableVector>::value,
+              "!pybind11::detail::is_copy_assignable<NotCopyableNotMovableVector>::value");
+
+struct NotMovableMap : std::map<int, NotMovable> {};
+static_assert(std::is_move_constructible<NotMovableMap>::value,
+              "std::is_move_constructible<NotMovableMap>::value");
+static_assert(std::is_copy_constructible<NotMovableMap>::value,
+              "std::is_copy_constructible<NotMovableMap>::value");
+static_assert(!pybind11::detail::is_move_constructible<NotMovableMap>::value,
+              "!pybind11::detail::is_move_constructible<NotMovableMap>::value");
+static_assert(pybind11::detail::is_copy_constructible<NotMovableMap>::value,
+              "pybind11::detail::is_copy_constructible<NotMovableMap>::value");
+static_assert(std::is_move_assignable<NotMovableMap>::value,
+              "std::is_move_assignable<NotMovableMap>::value");
+static_assert(std::is_copy_assignable<NotMovableMap>::value,
+              "std::is_copy_assignable<NotMovableMap>::value");
+// pybind11 does not have this
+// static_assert(!pybind11::detail::is_move_assignable<NotMovableMap>::value,
+//               "!pybind11::detail::is_move_assignable<NotMovableMap>::value");
+static_assert(pybind11::detail::is_copy_assignable<NotMovableMap>::value,
+              "pybind11::detail::is_copy_assignable<NotMovableMap>::value");
+
+struct NotCopyableMap : std::map<int, NotCopyable> {};
+static_assert(std::is_move_constructible<NotCopyableMap>::value,
+              "std::is_move_constructible<NotCopyableMap>::value");
+static_assert(std::is_copy_constructible<NotCopyableMap>::value,
+              "std::is_copy_constructible<NotCopyableMap>::value");
+static_assert(pybind11::detail::is_move_constructible<NotCopyableMap>::value,
+              "pybind11::detail::is_move_constructible<NotCopyableMap>::value");
+static_assert(!pybind11::detail::is_copy_constructible<NotCopyableMap>::value,
+              "!pybind11::detail::is_copy_constructible<NotCopyableMap>::value");
+static_assert(std::is_move_assignable<NotCopyableMap>::value,
+              "std::is_move_assignable<NotCopyableMap>::value");
+static_assert(std::is_copy_assignable<NotCopyableMap>::value,
+              "std::is_copy_assignable<NotCopyableMap>::value");
+// pybind11 does not have this
+// static_assert(!pybind11::detail::is_move_assignable<NotCopyableMap>::value,
+//               "!pybind11::detail::is_move_assignable<NotCopyableMap>::value");
+static_assert(!pybind11::detail::is_copy_assignable<NotCopyableMap>::value,
+              "!pybind11::detail::is_copy_assignable<NotCopyableMap>::value");
+
+struct NotCopyableNotMovableMap : std::map<int, NotCopyableNotMovable> {};
+static_assert(std::is_move_constructible<NotCopyableNotMovableMap>::value,
+              "std::is_move_constructible<NotCopyableNotMovableMap>::value");
+static_assert(std::is_copy_constructible<NotCopyableNotMovableMap>::value,
+              "std::is_copy_constructible<NotCopyableNotMovableMap>::value");
+static_assert(!pybind11::detail::is_move_constructible<NotCopyableNotMovableMap>::value,
+              "!pybind11::detail::is_move_constructible<NotCopyableNotMovableMap>::value");
+static_assert(!pybind11::detail::is_copy_constructible<NotCopyableNotMovableMap>::value,
+              "!pybind11::detail::is_copy_constructible<NotCopyableNotMovableMap>::value");
+static_assert(std::is_move_assignable<NotCopyableNotMovableMap>::value,
+              "std::is_move_assignable<NotCopyableNotMovableMap>::value");
+static_assert(std::is_copy_assignable<NotCopyableNotMovableMap>::value,
+              "std::is_copy_assignable<NotCopyableNotMovableMap>::value");
+// pybind11 does not have this
+// static_assert(!pybind11::detail::is_move_assignable<NotCopyableNotMovableMap>::value,
+//               "!pybind11::detail::is_move_assignable<NotCopyableNotMovableMap>::value");
+static_assert(!pybind11::detail::is_copy_assignable<NotCopyableNotMovableMap>::value,
+              "!pybind11::detail::is_copy_assignable<NotCopyableNotMovableMap>::value");
+
+struct RecursiveVector : std::vector<RecursiveVector> {};
+static_assert(std::is_move_constructible<RecursiveVector>::value,
+              "std::is_move_constructible<RecursiveVector>::value");
+static_assert(std::is_copy_constructible<RecursiveVector>::value,
+              "std::is_copy_constructible<RecursiveVector>::value");
+static_assert(pybind11::detail::is_move_constructible<RecursiveVector>::value,
+              "pybind11::detail::is_move_constructible<RecursiveVector>::value");
+static_assert(pybind11::detail::is_copy_constructible<RecursiveVector>::value,
+              "pybind11::detail::is_copy_constructible<RecursiveVector>::value");
+static_assert(std::is_move_assignable<RecursiveVector>::value,
+              "std::is_move_assignable<RecursiveVector>::value");
+static_assert(std::is_copy_assignable<RecursiveVector>::value,
+              "std::is_copy_assignable<RecursiveVector>::value");
+// pybind11 does not have this
+// static_assert(!pybind11::detail::is_move_assignable<RecursiveVector>::value,
+//               "!pybind11::detail::is_move_assignable<RecursiveVector>::value");
+static_assert(pybind11::detail::is_copy_assignable<RecursiveVector>::value,
+              "pybind11::detail::is_copy_assignable<RecursiveVector>::value");
+
+struct RecursiveMap : std::map<int, RecursiveMap> {};
+static_assert(std::is_move_constructible<RecursiveMap>::value,
+              "std::is_move_constructible<RecursiveMap>::value");
+static_assert(std::is_copy_constructible<RecursiveMap>::value,
+              "std::is_copy_constructible<RecursiveMap>::value");
+static_assert(pybind11::detail::is_move_constructible<RecursiveMap>::value,
+              "pybind11::detail::is_move_constructible<RecursiveMap>::value");
+static_assert(pybind11::detail::is_copy_constructible<RecursiveMap>::value,
+              "pybind11::detail::is_copy_constructible<RecursiveMap>::value");
+static_assert(std::is_move_assignable<RecursiveMap>::value,
+              "std::is_move_assignable<RecursiveMap>::value");
+static_assert(std::is_copy_assignable<RecursiveMap>::value,
+              "std::is_copy_assignable<RecursiveMap>::value");
+// pybind11 does not have this
+// static_assert(!pybind11::detail::is_move_assignable<RecursiveMap>::value,
+//               "!pybind11::detail::is_move_assignable<RecursiveMap>::value");
+static_assert(pybind11::detail::is_copy_assignable<RecursiveMap>::value,
+              "pybind11::detail::is_copy_assignable<RecursiveMap>::value");
diff --git a/wrap/pybind11/tests/test_custom_type_casters.cpp b/wrap/pybind11/tests/test_custom_type_casters.cpp
index 25540e368..b4af02a45 100644
--- a/wrap/pybind11/tests/test_custom_type_casters.cpp
+++ b/wrap/pybind11/tests/test_custom_type_casters.cpp
@@ -21,7 +21,7 @@ public:
 };
 class ArgAlwaysConverts {};
 
-namespace pybind11 {
+namespace PYBIND11_NAMESPACE {
 namespace detail {
 template <>
 struct type_caster<ArgInspector1> {
@@ -74,7 +74,7 @@ public:
     }
 };
 } // namespace detail
-} // namespace pybind11
+} // namespace PYBIND11_NAMESPACE
 
 // test_custom_caster_destruction
 class DestructionTester {
@@ -92,7 +92,7 @@ public:
         return *this;
     }
 };
-namespace pybind11 {
+namespace PYBIND11_NAMESPACE {
 namespace detail {
 template <>
 struct type_caster<DestructionTester> {
@@ -104,7 +104,7 @@ struct type_caster<DestructionTester> {
     }
 };
 } // namespace detail
-} // namespace pybind11
+} // namespace PYBIND11_NAMESPACE
 
 // Define type caster outside of `pybind11::detail` and then alias it.
 namespace other_lib {
@@ -112,7 +112,7 @@ struct MyType {};
 // Corrupt `py` shorthand alias for surrounding context.
 namespace py {}
 // Corrupt unqualified relative `pybind11` namespace.
-namespace pybind11 {}
+namespace PYBIND11_NAMESPACE {}
 // Correct alias.
 namespace py_ = ::pybind11;
 // Define caster. This is effectively no-op, we only ensure it compiles and we
@@ -127,12 +127,12 @@ struct my_caster {
 };
 } // namespace other_lib
 // Effectively "alias" it into correct namespace (via inheritance).
-namespace pybind11 {
+namespace PYBIND11_NAMESPACE {
 namespace detail {
 template <>
 struct type_caster<other_lib::MyType> : public other_lib::my_caster {};
 } // namespace detail
-} // namespace pybind11
+} // namespace PYBIND11_NAMESPACE
 
 TEST_SUBMODULE(custom_type_casters, m) {
     // test_custom_type_casters
diff --git a/wrap/pybind11/tests/test_custom_type_casters.py b/wrap/pybind11/tests/test_custom_type_casters.py
index adfa6cf86..3a00ea964 100644
--- a/wrap/pybind11/tests/test_custom_type_casters.py
+++ b/wrap/pybind11/tests/test_custom_type_casters.py
@@ -94,12 +94,14 @@ def test_noconvert_args(msg):
 
 def test_custom_caster_destruction():
     """Tests that returning a pointer to a type that gets converted with a custom type caster gets
-    destroyed when the function has py::return_value_policy::take_ownership policy applied."""
+    destroyed when the function has py::return_value_policy::take_ownership policy applied.
+    """
 
     cstats = m.destruction_tester_cstats()
     # This one *doesn't* have take_ownership: the pointer should be used but not destroyed:
     z = m.custom_caster_no_destroy()
-    assert cstats.alive() == 1 and cstats.default_constructions == 1
+    assert cstats.alive() == 1
+    assert cstats.default_constructions == 1
     assert z
 
     # take_ownership applied: this constructs a new object, casts it, then destroys it:
diff --git a/wrap/pybind11/tests/test_custom_type_setup.py b/wrap/pybind11/tests/test_custom_type_setup.py
index 19b44c9de..e63ff5758 100644
--- a/wrap/pybind11/tests/test_custom_type_setup.py
+++ b/wrap/pybind11/tests/test_custom_type_setup.py
@@ -7,7 +7,7 @@ import env  # noqa: F401
 from pybind11_tests import custom_type_setup as m
 
 
-@pytest.fixture
+@pytest.fixture()
 def gc_tester():
     """Tests that an object is garbage collected.
 
diff --git a/wrap/pybind11/tests/test_docstring_options.cpp b/wrap/pybind11/tests/test_docstring_options.cpp
index 4d44f4e20..dda1cf6e4 100644
--- a/wrap/pybind11/tests/test_docstring_options.cpp
+++ b/wrap/pybind11/tests/test_docstring_options.cpp
@@ -85,4 +85,57 @@ TEST_SUBMODULE(docstring_options, m) {
                           &DocstringTestFoo::setValue,
                           "This is a property docstring");
     }
+
+    {
+        enum class DocstringTestEnum1 { Member1, Member2 };
+
+        py::enum_<DocstringTestEnum1>(m, "DocstringTestEnum1", "Enum docstring")
+            .value("Member1", DocstringTestEnum1::Member1)
+            .value("Member2", DocstringTestEnum1::Member2);
+    }
+
+    {
+        py::options options;
+        options.enable_enum_members_docstring();
+
+        enum class DocstringTestEnum2 { Member1, Member2 };
+
+        py::enum_<DocstringTestEnum2>(m, "DocstringTestEnum2", "Enum docstring")
+            .value("Member1", DocstringTestEnum2::Member1)
+            .value("Member2", DocstringTestEnum2::Member2);
+    }
+
+    {
+        py::options options;
+        options.disable_enum_members_docstring();
+
+        enum class DocstringTestEnum3 { Member1, Member2 };
+
+        py::enum_<DocstringTestEnum3>(m, "DocstringTestEnum3", "Enum docstring")
+            .value("Member1", DocstringTestEnum3::Member1)
+            .value("Member2", DocstringTestEnum3::Member2);
+    }
+
+    {
+        py::options options;
+        options.disable_user_defined_docstrings();
+
+        enum class DocstringTestEnum4 { Member1, Member2 };
+
+        py::enum_<DocstringTestEnum4>(m, "DocstringTestEnum4", "Enum docstring")
+            .value("Member1", DocstringTestEnum4::Member1)
+            .value("Member2", DocstringTestEnum4::Member2);
+    }
+
+    {
+        py::options options;
+        options.disable_user_defined_docstrings();
+        options.disable_enum_members_docstring();
+
+        enum class DocstringTestEnum5 { Member1, Member2 };
+
+        py::enum_<DocstringTestEnum5>(m, "DocstringTestEnum5", "Enum docstring")
+            .value("Member1", DocstringTestEnum5::Member1)
+            .value("Member2", DocstringTestEnum5::Member2);
+    }
 }
diff --git a/wrap/pybind11/tests/test_docstring_options.py b/wrap/pybind11/tests/test_docstring_options.py
index fcd16b89f..e6f5a9d98 100644
--- a/wrap/pybind11/tests/test_docstring_options.py
+++ b/wrap/pybind11/tests/test_docstring_options.py
@@ -39,3 +39,26 @@ def test_docstring_options():
     # Suppression of user-defined docstrings for non-function objects
     assert not m.DocstringTestFoo.__doc__
     assert not m.DocstringTestFoo.value_prop.__doc__
+
+    # Check existig behaviour of enum docstings
+    assert (
+        m.DocstringTestEnum1.__doc__
+        == "Enum docstring\n\nMembers:\n\n  Member1\n\n  Member2"
+    )
+
+    # options.enable_enum_members_docstring()
+    assert (
+        m.DocstringTestEnum2.__doc__
+        == "Enum docstring\n\nMembers:\n\n  Member1\n\n  Member2"
+    )
+
+    # options.disable_enum_members_docstring()
+    assert m.DocstringTestEnum3.__doc__ == "Enum docstring"
+
+    # options.disable_user_defined_docstrings()
+    assert m.DocstringTestEnum4.__doc__ == "Members:\n\n  Member1\n\n  Member2"
+
+    # options.disable_user_defined_docstrings()
+    # options.disable_enum_members_docstring()
+    # When all options are disabled, no docstring (instead of an empty one) should be generated
+    assert m.DocstringTestEnum5.__doc__ is None
diff --git a/wrap/pybind11/tests/test_eigen_matrix.cpp b/wrap/pybind11/tests/test_eigen_matrix.cpp
new file mode 100644
index 000000000..554cc4d7f
--- /dev/null
+++ b/wrap/pybind11/tests/test_eigen_matrix.cpp
@@ -0,0 +1,428 @@
+/*
+    tests/eigen.cpp -- automatic conversion of Eigen types
+
+    Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#include <pybind11/eigen/matrix.h>
+#include <pybind11/stl.h>
+
+#include "constructor_stats.h"
+#include "pybind11_tests.h"
+
+PYBIND11_WARNING_DISABLE_MSVC(4996)
+
+#include <Eigen/Cholesky>
+
+using MatrixXdR = Eigen::Matrix<double, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor>;
+
+// Sets/resets a testing reference matrix to have values of 10*r + c, where r and c are the
+// (1-based) row/column number.
+template <typename M>
+void reset_ref(M &x) {
+    for (int i = 0; i < x.rows(); i++) {
+        for (int j = 0; j < x.cols(); j++) {
+            x(i, j) = 11 + 10 * i + j;
+        }
+    }
+}
+
+// Returns a static, column-major matrix
+Eigen::MatrixXd &get_cm() {
+    static Eigen::MatrixXd *x;
+    if (!x) {
+        x = new Eigen::MatrixXd(3, 3);
+        reset_ref(*x);
+    }
+    return *x;
+}
+// Likewise, but row-major
+MatrixXdR &get_rm() {
+    static MatrixXdR *x;
+    if (!x) {
+        x = new MatrixXdR(3, 3);
+        reset_ref(*x);
+    }
+    return *x;
+}
+// Resets the values of the static matrices returned by get_cm()/get_rm()
+void reset_refs() {
+    reset_ref(get_cm());
+    reset_ref(get_rm());
+}
+
+// Returns element 2,1 from a matrix (used to test copy/nocopy)
+double get_elem(const Eigen::Ref<const Eigen::MatrixXd> &m) { return m(2, 1); };
+
+// Returns a matrix with 10*r + 100*c added to each matrix element (to help test that the matrix
+// reference is referencing rows/columns correctly).
+template <typename MatrixArgType>
+Eigen::MatrixXd adjust_matrix(MatrixArgType m) {
+    Eigen::MatrixXd ret(m);
+    for (int c = 0; c < m.cols(); c++) {
+        for (int r = 0; r < m.rows(); r++) {
+            ret(r, c) += 10 * r + 100 * c; // NOLINT(clang-analyzer-core.uninitialized.Assign)
+        }
+    }
+    return ret;
+}
+
+struct CustomOperatorNew {
+    CustomOperatorNew() = default;
+
+    Eigen::Matrix4d a = Eigen::Matrix4d::Zero();
+    Eigen::Matrix4d b = Eigen::Matrix4d::Identity();
+
+    EIGEN_MAKE_ALIGNED_OPERATOR_NEW;
+};
+
+TEST_SUBMODULE(eigen_matrix, m) {
+    using FixedMatrixR = Eigen::Matrix<float, 5, 6, Eigen::RowMajor>;
+    using FixedMatrixC = Eigen::Matrix<float, 5, 6>;
+    using DenseMatrixR = Eigen::Matrix<float, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor>;
+    using DenseMatrixC = Eigen::Matrix<float, Eigen::Dynamic, Eigen::Dynamic>;
+    using FourRowMatrixC = Eigen::Matrix<float, 4, Eigen::Dynamic>;
+    using FourColMatrixC = Eigen::Matrix<float, Eigen::Dynamic, 4>;
+    using FourRowMatrixR = Eigen::Matrix<float, 4, Eigen::Dynamic>;
+    using FourColMatrixR = Eigen::Matrix<float, Eigen::Dynamic, 4>;
+    using SparseMatrixR = Eigen::SparseMatrix<float, Eigen::RowMajor>;
+    using SparseMatrixC = Eigen::SparseMatrix<float>;
+
+    // various tests
+    m.def("double_col", [](const Eigen::VectorXf &x) -> Eigen::VectorXf { return 2.0f * x; });
+    m.def("double_row",
+          [](const Eigen::RowVectorXf &x) -> Eigen::RowVectorXf { return 2.0f * x; });
+    m.def("double_complex",
+          [](const Eigen::VectorXcf &x) -> Eigen::VectorXcf { return 2.0f * x; });
+    m.def("double_threec", [](py::EigenDRef<Eigen::Vector3f> x) { x *= 2; });
+    m.def("double_threer", [](py::EigenDRef<Eigen::RowVector3f> x) { x *= 2; });
+    m.def("double_mat_cm", [](const Eigen::MatrixXf &x) -> Eigen::MatrixXf { return 2.0f * x; });
+    m.def("double_mat_rm", [](const DenseMatrixR &x) -> DenseMatrixR { return 2.0f * x; });
+
+    // test_eigen_ref_to_python
+    // Different ways of passing via Eigen::Ref; the first and second are the Eigen-recommended
+    m.def("cholesky1",
+          [](const Eigen::Ref<MatrixXdR> &x) -> Eigen::MatrixXd { return x.llt().matrixL(); });
+    m.def("cholesky2", [](const Eigen::Ref<const MatrixXdR> &x) -> Eigen::MatrixXd {
+        return x.llt().matrixL();
+    });
+    m.def("cholesky3",
+          [](const Eigen::Ref<MatrixXdR> &x) -> Eigen::MatrixXd { return x.llt().matrixL(); });
+    m.def("cholesky4", [](const Eigen::Ref<const MatrixXdR> &x) -> Eigen::MatrixXd {
+        return x.llt().matrixL();
+    });
+
+    // test_eigen_ref_mutators
+    // Mutators: these add some value to the given element using Eigen, but Eigen should be mapping
+    // into the numpy array data and so the result should show up there.  There are three versions:
+    // one that works on a contiguous-row matrix (numpy's default), one for a contiguous-column
+    // matrix, and one for any matrix.
+    auto add_rm = [](Eigen::Ref<MatrixXdR> x, int r, int c, double v) { x(r, c) += v; };
+    auto add_cm = [](Eigen::Ref<Eigen::MatrixXd> x, int r, int c, double v) { x(r, c) += v; };
+
+    // Mutators (Eigen maps into numpy variables):
+    m.def("add_rm", add_rm); // Only takes row-contiguous
+    m.def("add_cm", add_cm); // Only takes column-contiguous
+    // Overloaded versions that will accept either row or column contiguous:
+    m.def("add1", add_rm);
+    m.def("add1", add_cm);
+    m.def("add2", add_cm);
+    m.def("add2", add_rm);
+    // This one accepts a matrix of any stride:
+    m.def("add_any",
+          [](py::EigenDRef<Eigen::MatrixXd> x, int r, int c, double v) { x(r, c) += v; });
+
+    // Return mutable references (numpy maps into eigen variables)
+    m.def("get_cm_ref", []() { return Eigen::Ref<Eigen::MatrixXd>(get_cm()); });
+    m.def("get_rm_ref", []() { return Eigen::Ref<MatrixXdR>(get_rm()); });
+    // The same references, but non-mutable (numpy maps into eigen variables, but is !writeable)
+    m.def("get_cm_const_ref", []() { return Eigen::Ref<const Eigen::MatrixXd>(get_cm()); });
+    m.def("get_rm_const_ref", []() { return Eigen::Ref<const MatrixXdR>(get_rm()); });
+
+    m.def("reset_refs", reset_refs); // Restores get_{cm,rm}_ref to original values
+
+    // Increments and returns ref to (same) matrix
+    m.def(
+        "incr_matrix",
+        [](Eigen::Ref<Eigen::MatrixXd> m, double v) {
+            m += Eigen::MatrixXd::Constant(m.rows(), m.cols(), v);
+            return m;
+        },
+        py::return_value_policy::reference);
+
+    // Same, but accepts a matrix of any strides
+    m.def(
+        "incr_matrix_any",
+        [](py::EigenDRef<Eigen::MatrixXd> m, double v) {
+            m += Eigen::MatrixXd::Constant(m.rows(), m.cols(), v);
+            return m;
+        },
+        py::return_value_policy::reference);
+
+    // Returns an eigen slice of even rows
+    m.def(
+        "even_rows",
+        [](py::EigenDRef<Eigen::MatrixXd> m) {
+            return py::EigenDMap<Eigen::MatrixXd>(
+                m.data(),
+                (m.rows() + 1) / 2,
+                m.cols(),
+                py::EigenDStride(m.outerStride(), 2 * m.innerStride()));
+        },
+        py::return_value_policy::reference);
+
+    // Returns an eigen slice of even columns
+    m.def(
+        "even_cols",
+        [](py::EigenDRef<Eigen::MatrixXd> m) {
+            return py::EigenDMap<Eigen::MatrixXd>(
+                m.data(),
+                m.rows(),
+                (m.cols() + 1) / 2,
+                py::EigenDStride(2 * m.outerStride(), m.innerStride()));
+        },
+        py::return_value_policy::reference);
+
+    // Returns diagonals: a vector-like object with an inner stride != 1
+    m.def("diagonal", [](const Eigen::Ref<const Eigen::MatrixXd> &x) { return x.diagonal(); });
+    m.def("diagonal_1",
+          [](const Eigen::Ref<const Eigen::MatrixXd> &x) { return x.diagonal<1>(); });
+    m.def("diagonal_n",
+          [](const Eigen::Ref<const Eigen::MatrixXd> &x, int index) { return x.diagonal(index); });
+
+    // Return a block of a matrix (gives non-standard strides)
+    m.def("block",
+          [m](const py::object &x_obj,
+              int start_row,
+              int start_col,
+              int block_rows,
+              int block_cols) {
+              return m.attr("_block")(x_obj, x_obj, start_row, start_col, block_rows, block_cols);
+          });
+
+    m.def(
+        "_block",
+        [](const py::object &x_obj,
+           const Eigen::Ref<const Eigen::MatrixXd> &x,
+           int start_row,
+           int start_col,
+           int block_rows,
+           int block_cols) {
+            // See PR #4217 for background. This test is a bit over the top, but might be useful
+            // as a concrete example to point to when explaining the dangling reference trap.
+            auto i0 = py::make_tuple(0, 0);
+            auto x0_orig = x_obj[*i0].cast<double>();
+            if (x(0, 0) != x0_orig) {
+                throw std::runtime_error(
+                    "Something in the type_caster for Eigen::Ref is terribly wrong.");
+            }
+            double x0_mod = x0_orig + 1;
+            x_obj[*i0] = x0_mod;
+            auto copy_detected = (x(0, 0) != x0_mod);
+            x_obj[*i0] = x0_orig;
+            if (copy_detected) {
+                throw std::runtime_error("type_caster for Eigen::Ref made a copy.");
+            }
+            return x.block(start_row, start_col, block_rows, block_cols);
+        },
+        py::keep_alive<0, 1>());
+
+    // test_eigen_return_references, test_eigen_keepalive
+    // return value referencing/copying tests:
+    class ReturnTester {
+        Eigen::MatrixXd mat = create();
+
+    public:
+        ReturnTester() { print_created(this); }
+        ~ReturnTester() { print_destroyed(this); }
+        static Eigen::MatrixXd create() { return Eigen::MatrixXd::Ones(10, 10); }
+        // NOLINTNEXTLINE(readability-const-return-type)
+        static const Eigen::MatrixXd createConst() { return Eigen::MatrixXd::Ones(10, 10); }
+        Eigen::MatrixXd &get() { return mat; }
+        Eigen::MatrixXd *getPtr() { return &mat; }
+        const Eigen::MatrixXd &view() { return mat; }
+        const Eigen::MatrixXd *viewPtr() { return &mat; }
+        Eigen::Ref<Eigen::MatrixXd> ref() { return mat; }
+        Eigen::Ref<const Eigen::MatrixXd> refConst() { return mat; }
+        Eigen::Block<Eigen::MatrixXd> block(int r, int c, int nrow, int ncol) {
+            return mat.block(r, c, nrow, ncol);
+        }
+        Eigen::Block<const Eigen::MatrixXd> blockConst(int r, int c, int nrow, int ncol) const {
+            return mat.block(r, c, nrow, ncol);
+        }
+        py::EigenDMap<Eigen::Matrix2d> corners() {
+            return py::EigenDMap<Eigen::Matrix2d>(
+                mat.data(),
+                py::EigenDStride(mat.outerStride() * (mat.outerSize() - 1),
+                                 mat.innerStride() * (mat.innerSize() - 1)));
+        }
+        py::EigenDMap<const Eigen::Matrix2d> cornersConst() const {
+            return py::EigenDMap<const Eigen::Matrix2d>(
+                mat.data(),
+                py::EigenDStride(mat.outerStride() * (mat.outerSize() - 1),
+                                 mat.innerStride() * (mat.innerSize() - 1)));
+        }
+    };
+    using rvp = py::return_value_policy;
+    py::class_<ReturnTester>(m, "ReturnTester")
+        .def(py::init<>())
+        .def_static("create", &ReturnTester::create)
+        .def_static("create_const", &ReturnTester::createConst)
+        .def("get", &ReturnTester::get, rvp::reference_internal)
+        .def("get_ptr", &ReturnTester::getPtr, rvp::reference_internal)
+        .def("view", &ReturnTester::view, rvp::reference_internal)
+        .def("view_ptr", &ReturnTester::view, rvp::reference_internal)
+        .def("copy_get", &ReturnTester::get)       // Default rvp: copy
+        .def("copy_view", &ReturnTester::view)     //         "
+        .def("ref", &ReturnTester::ref)            // Default for Ref is to reference
+        .def("ref_const", &ReturnTester::refConst) // Likewise, but const
+        .def("ref_safe", &ReturnTester::ref, rvp::reference_internal)
+        .def("ref_const_safe", &ReturnTester::refConst, rvp::reference_internal)
+        .def("copy_ref", &ReturnTester::ref, rvp::copy)
+        .def("copy_ref_const", &ReturnTester::refConst, rvp::copy)
+        .def("block", &ReturnTester::block)
+        .def("block_safe", &ReturnTester::block, rvp::reference_internal)
+        .def("block_const", &ReturnTester::blockConst, rvp::reference_internal)
+        .def("copy_block", &ReturnTester::block, rvp::copy)
+        .def("corners", &ReturnTester::corners, rvp::reference_internal)
+        .def("corners_const", &ReturnTester::cornersConst, rvp::reference_internal);
+
+    // test_special_matrix_objects
+    // Returns a DiagonalMatrix with diagonal (1,2,3,...)
+    m.def("incr_diag", [](int k) {
+        Eigen::DiagonalMatrix<int, Eigen::Dynamic> m(k);
+        for (int i = 0; i < k; i++) {
+            m.diagonal()[i] = i + 1;
+        }
+        return m;
+    });
+
+    // Returns a SelfAdjointView referencing the lower triangle of m
+    m.def("symmetric_lower",
+          [](const Eigen::MatrixXi &m) { return m.selfadjointView<Eigen::Lower>(); });
+    // Returns a SelfAdjointView referencing the lower triangle of m
+    m.def("symmetric_upper",
+          [](const Eigen::MatrixXi &m) { return m.selfadjointView<Eigen::Upper>(); });
+
+    // Test matrix for various functions below.
+    Eigen::MatrixXf mat(5, 6);
+    mat << 0, 3, 0, 0, 0, 11, 22, 0, 0, 0, 17, 11, 7, 5, 0, 1, 0, 11, 0, 0, 0, 0, 0, 11, 0, 0, 14,
+        0, 8, 11;
+
+    // test_fixed, and various other tests
+    m.def("fixed_r", [mat]() -> FixedMatrixR { return FixedMatrixR(mat); });
+    // Our Eigen does a hack which respects constness through the numpy writeable flag.
+    // Therefore, the const return actually affects this type despite being an rvalue.
+    // NOLINTNEXTLINE(readability-const-return-type)
+    m.def("fixed_r_const", [mat]() -> const FixedMatrixR { return FixedMatrixR(mat); });
+    m.def("fixed_c", [mat]() -> FixedMatrixC { return FixedMatrixC(mat); });
+    m.def("fixed_copy_r", [](const FixedMatrixR &m) -> FixedMatrixR { return m; });
+    m.def("fixed_copy_c", [](const FixedMatrixC &m) -> FixedMatrixC { return m; });
+    // test_mutator_descriptors
+    m.def("fixed_mutator_r", [](const Eigen::Ref<FixedMatrixR> &) {});
+    m.def("fixed_mutator_c", [](const Eigen::Ref<FixedMatrixC> &) {});
+    m.def("fixed_mutator_a", [](const py::EigenDRef<FixedMatrixC> &) {});
+    // test_dense
+    m.def("dense_r", [mat]() -> DenseMatrixR { return DenseMatrixR(mat); });
+    m.def("dense_c", [mat]() -> DenseMatrixC { return DenseMatrixC(mat); });
+    m.def("dense_copy_r", [](const DenseMatrixR &m) -> DenseMatrixR { return m; });
+    m.def("dense_copy_c", [](const DenseMatrixC &m) -> DenseMatrixC { return m; });
+    // test_sparse, test_sparse_signature
+    m.def("sparse_r", [mat]() -> SparseMatrixR {
+        // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn)
+        return Eigen::SparseView<Eigen::MatrixXf>(mat);
+    });
+    m.def("sparse_c",
+          [mat]() -> SparseMatrixC { return Eigen::SparseView<Eigen::MatrixXf>(mat); });
+    m.def("sparse_copy_r", [](const SparseMatrixR &m) -> SparseMatrixR { return m; });
+    m.def("sparse_copy_c", [](const SparseMatrixC &m) -> SparseMatrixC { return m; });
+    // test_partially_fixed
+    m.def("partial_copy_four_rm_r", [](const FourRowMatrixR &m) -> FourRowMatrixR { return m; });
+    m.def("partial_copy_four_rm_c", [](const FourColMatrixR &m) -> FourColMatrixR { return m; });
+    m.def("partial_copy_four_cm_r", [](const FourRowMatrixC &m) -> FourRowMatrixC { return m; });
+    m.def("partial_copy_four_cm_c", [](const FourColMatrixC &m) -> FourColMatrixC { return m; });
+
+    // test_cpp_casting
+    // Test that we can cast a numpy object to a Eigen::MatrixXd explicitly
+    m.def("cpp_copy", [](py::handle m) { return m.cast<Eigen::MatrixXd>()(1, 0); });
+    m.def("cpp_ref_c", [](py::handle m) { return m.cast<Eigen::Ref<Eigen::MatrixXd>>()(1, 0); });
+    m.def("cpp_ref_r", [](py::handle m) { return m.cast<Eigen::Ref<MatrixXdR>>()(1, 0); });
+    m.def("cpp_ref_any",
+          [](py::handle m) { return m.cast<py::EigenDRef<Eigen::MatrixXd>>()(1, 0); });
+
+    // [workaround(intel)] ICC 20/21 breaks with py::arg().stuff, using py::arg{}.stuff works.
+
+    // test_nocopy_wrapper
+    // Test that we can prevent copying into an argument that would normally copy: First a version
+    // that would allow copying (if types or strides don't match) for comparison:
+    m.def("get_elem", &get_elem);
+    // Now this alternative that calls the tells pybind to fail rather than copy:
+    m.def(
+        "get_elem_nocopy",
+        [](const Eigen::Ref<const Eigen::MatrixXd> &m) -> double { return get_elem(m); },
+        py::arg{}.noconvert());
+    // Also test a row-major-only no-copy const ref:
+    m.def(
+        "get_elem_rm_nocopy",
+        [](Eigen::Ref<const Eigen::Matrix<long, -1, -1, Eigen::RowMajor>> &m) -> long {
+            return m(2, 1);
+        },
+        py::arg{}.noconvert());
+
+    // test_issue738, test_zero_length
+    // Issue #738: 1×N or N×1 2D matrices were neither accepted nor properly copied with an
+    // incompatible stride value on the length-1 dimension--but that should be allowed (without
+    // requiring a copy!) because the stride value can be safely ignored on a size-1 dimension.
+    // Similarly, 0×N or N×0 matrices were not accepted--again, these should be allowed since
+    // they contain no data. This particularly affects numpy ≥ 1.23, which sets the strides to
+    // 0 if any dimension size is 0.
+    m.def("iss738_f1",
+          &adjust_matrix<const Eigen::Ref<const Eigen::MatrixXd> &>,
+          py::arg{}.noconvert());
+    m.def("iss738_f2",
+          &adjust_matrix<const Eigen::Ref<const Eigen::Matrix<double, -1, -1, Eigen::RowMajor>> &>,
+          py::arg{}.noconvert());
+
+    // test_issue1105
+    // Issue #1105: when converting from a numpy two-dimensional (Nx1) or (1xN) value into a dense
+    // eigen Vector or RowVector, the argument would fail to load because the numpy copy would
+    // fail: numpy won't broadcast a Nx1 into a 1-dimensional vector.
+    m.def("iss1105_col", [](const Eigen::VectorXd &) { return true; });
+    m.def("iss1105_row", [](const Eigen::RowVectorXd &) { return true; });
+
+    // test_named_arguments
+    // Make sure named arguments are working properly:
+    m.def(
+        "matrix_multiply",
+        [](const py::EigenDRef<const Eigen::MatrixXd> &A,
+           const py::EigenDRef<const Eigen::MatrixXd> &B) -> Eigen::MatrixXd {
+            if (A.cols() != B.rows()) {
+                throw std::domain_error("Nonconformable matrices!");
+            }
+            return A * B;
+        },
+        py::arg("A"),
+        py::arg("B"));
+
+    // test_custom_operator_new
+    py::class_<CustomOperatorNew>(m, "CustomOperatorNew")
+        .def(py::init<>())
+        .def_readonly("a", &CustomOperatorNew::a)
+        .def_readonly("b", &CustomOperatorNew::b);
+
+    // test_eigen_ref_life_support
+    // In case of a failure (the caster's temp array does not live long enough), creating
+    // a new array (np.ones(10)) increases the chances that the temp array will be garbage
+    // collected and/or that its memory will be overridden with different values.
+    m.def("get_elem_direct", [](const Eigen::Ref<const Eigen::VectorXd> &v) {
+        py::module_::import("numpy").attr("ones")(10);
+        return v(5);
+    });
+    m.def("get_elem_indirect", [](std::vector<Eigen::Ref<const Eigen::VectorXd>> v) {
+        py::module_::import("numpy").attr("ones")(10);
+        return v[0](5);
+    });
+}
diff --git a/wrap/pybind11/tests/test_eigen_matrix.py b/wrap/pybind11/tests/test_eigen_matrix.py
new file mode 100644
index 000000000..b2e76740b
--- /dev/null
+++ b/wrap/pybind11/tests/test_eigen_matrix.py
@@ -0,0 +1,807 @@
+import pytest
+
+from pybind11_tests import ConstructorStats
+
+np = pytest.importorskip("numpy")
+m = pytest.importorskip("pybind11_tests.eigen_matrix")
+
+
+ref = np.array(
+    [
+        [0.0, 3, 0, 0, 0, 11],
+        [22, 0, 0, 0, 17, 11],
+        [7, 5, 0, 1, 0, 11],
+        [0, 0, 0, 0, 0, 11],
+        [0, 0, 14, 0, 8, 11],
+    ]
+)
+
+
+def assert_equal_ref(mat):
+    np.testing.assert_array_equal(mat, ref)
+
+
+def assert_sparse_equal_ref(sparse_mat):
+    assert_equal_ref(sparse_mat.toarray())
+
+
+def test_fixed():
+    assert_equal_ref(m.fixed_c())
+    assert_equal_ref(m.fixed_r())
+    assert_equal_ref(m.fixed_copy_r(m.fixed_r()))
+    assert_equal_ref(m.fixed_copy_c(m.fixed_c()))
+    assert_equal_ref(m.fixed_copy_r(m.fixed_c()))
+    assert_equal_ref(m.fixed_copy_c(m.fixed_r()))
+
+
+def test_dense():
+    assert_equal_ref(m.dense_r())
+    assert_equal_ref(m.dense_c())
+    assert_equal_ref(m.dense_copy_r(m.dense_r()))
+    assert_equal_ref(m.dense_copy_c(m.dense_c()))
+    assert_equal_ref(m.dense_copy_r(m.dense_c()))
+    assert_equal_ref(m.dense_copy_c(m.dense_r()))
+
+
+def test_partially_fixed():
+    ref2 = np.array([[0.0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11], [12, 13, 14, 15]])
+    np.testing.assert_array_equal(m.partial_copy_four_rm_r(ref2), ref2)
+    np.testing.assert_array_equal(m.partial_copy_four_rm_c(ref2), ref2)
+    np.testing.assert_array_equal(m.partial_copy_four_rm_r(ref2[:, 1]), ref2[:, [1]])
+    np.testing.assert_array_equal(m.partial_copy_four_rm_c(ref2[0, :]), ref2[[0], :])
+    np.testing.assert_array_equal(
+        m.partial_copy_four_rm_r(ref2[:, (0, 2)]), ref2[:, (0, 2)]
+    )
+    np.testing.assert_array_equal(
+        m.partial_copy_four_rm_c(ref2[(3, 1, 2), :]), ref2[(3, 1, 2), :]
+    )
+
+    np.testing.assert_array_equal(m.partial_copy_four_cm_r(ref2), ref2)
+    np.testing.assert_array_equal(m.partial_copy_four_cm_c(ref2), ref2)
+    np.testing.assert_array_equal(m.partial_copy_four_cm_r(ref2[:, 1]), ref2[:, [1]])
+    np.testing.assert_array_equal(m.partial_copy_four_cm_c(ref2[0, :]), ref2[[0], :])
+    np.testing.assert_array_equal(
+        m.partial_copy_four_cm_r(ref2[:, (0, 2)]), ref2[:, (0, 2)]
+    )
+    np.testing.assert_array_equal(
+        m.partial_copy_four_cm_c(ref2[(3, 1, 2), :]), ref2[(3, 1, 2), :]
+    )
+
+    # TypeError should be raise for a shape mismatch
+    functions = [
+        m.partial_copy_four_rm_r,
+        m.partial_copy_four_rm_c,
+        m.partial_copy_four_cm_r,
+        m.partial_copy_four_cm_c,
+    ]
+    matrix_with_wrong_shape = [[1, 2], [3, 4]]
+    for f in functions:
+        with pytest.raises(TypeError) as excinfo:
+            f(matrix_with_wrong_shape)
+        assert "incompatible function arguments" in str(excinfo.value)
+
+
+def test_mutator_descriptors():
+    zr = np.arange(30, dtype="float32").reshape(5, 6)  # row-major
+    zc = zr.reshape(6, 5).transpose()  # column-major
+
+    m.fixed_mutator_r(zr)
+    m.fixed_mutator_c(zc)
+    m.fixed_mutator_a(zr)
+    m.fixed_mutator_a(zc)
+    with pytest.raises(TypeError) as excinfo:
+        m.fixed_mutator_r(zc)
+    assert (
+        "(arg0: numpy.ndarray[numpy.float32[5, 6],"
+        " flags.writeable, flags.c_contiguous]) -> None" in str(excinfo.value)
+    )
+    with pytest.raises(TypeError) as excinfo:
+        m.fixed_mutator_c(zr)
+    assert (
+        "(arg0: numpy.ndarray[numpy.float32[5, 6],"
+        " flags.writeable, flags.f_contiguous]) -> None" in str(excinfo.value)
+    )
+    with pytest.raises(TypeError) as excinfo:
+        m.fixed_mutator_a(np.array([[1, 2], [3, 4]], dtype="float32"))
+    assert "(arg0: numpy.ndarray[numpy.float32[5, 6], flags.writeable]) -> None" in str(
+        excinfo.value
+    )
+    zr.flags.writeable = False
+    with pytest.raises(TypeError):
+        m.fixed_mutator_r(zr)
+    with pytest.raises(TypeError):
+        m.fixed_mutator_a(zr)
+
+
+def test_cpp_casting():
+    assert m.cpp_copy(m.fixed_r()) == 22.0
+    assert m.cpp_copy(m.fixed_c()) == 22.0
+    z = np.array([[5.0, 6], [7, 8]])
+    assert m.cpp_copy(z) == 7.0
+    assert m.cpp_copy(m.get_cm_ref()) == 21.0
+    assert m.cpp_copy(m.get_rm_ref()) == 21.0
+    assert m.cpp_ref_c(m.get_cm_ref()) == 21.0
+    assert m.cpp_ref_r(m.get_rm_ref()) == 21.0
+    with pytest.raises(RuntimeError) as excinfo:
+        # Can't reference m.fixed_c: it contains floats, m.cpp_ref_any wants doubles
+        m.cpp_ref_any(m.fixed_c())
+    assert "Unable to cast Python instance" in str(excinfo.value)
+    with pytest.raises(RuntimeError) as excinfo:
+        # Can't reference m.fixed_r: it contains floats, m.cpp_ref_any wants doubles
+        m.cpp_ref_any(m.fixed_r())
+    assert "Unable to cast Python instance" in str(excinfo.value)
+    assert m.cpp_ref_any(m.ReturnTester.create()) == 1.0
+
+    assert m.cpp_ref_any(m.get_cm_ref()) == 21.0
+    assert m.cpp_ref_any(m.get_cm_ref()) == 21.0
+
+
+def test_pass_readonly_array():
+    z = np.full((5, 6), 42.0)
+    z.flags.writeable = False
+    np.testing.assert_array_equal(z, m.fixed_copy_r(z))
+    np.testing.assert_array_equal(m.fixed_r_const(), m.fixed_r())
+    assert not m.fixed_r_const().flags.writeable
+    np.testing.assert_array_equal(m.fixed_copy_r(m.fixed_r_const()), m.fixed_r_const())
+
+
+def test_nonunit_stride_from_python():
+    counting_mat = np.arange(9.0, dtype=np.float32).reshape((3, 3))
+    second_row = counting_mat[1, :]
+    second_col = counting_mat[:, 1]
+    np.testing.assert_array_equal(m.double_row(second_row), 2.0 * second_row)
+    np.testing.assert_array_equal(m.double_col(second_row), 2.0 * second_row)
+    np.testing.assert_array_equal(m.double_complex(second_row), 2.0 * second_row)
+    np.testing.assert_array_equal(m.double_row(second_col), 2.0 * second_col)
+    np.testing.assert_array_equal(m.double_col(second_col), 2.0 * second_col)
+    np.testing.assert_array_equal(m.double_complex(second_col), 2.0 * second_col)
+
+    counting_3d = np.arange(27.0, dtype=np.float32).reshape((3, 3, 3))
+    slices = [counting_3d[0, :, :], counting_3d[:, 0, :], counting_3d[:, :, 0]]
+    for ref_mat in slices:
+        np.testing.assert_array_equal(m.double_mat_cm(ref_mat), 2.0 * ref_mat)
+        np.testing.assert_array_equal(m.double_mat_rm(ref_mat), 2.0 * ref_mat)
+
+    # Mutator:
+    m.double_threer(second_row)
+    m.double_threec(second_col)
+    np.testing.assert_array_equal(counting_mat, [[0.0, 2, 2], [6, 16, 10], [6, 14, 8]])
+
+
+def test_negative_stride_from_python(msg):
+    """Eigen doesn't support (as of yet) negative strides. When a function takes an Eigen matrix by
+    copy or const reference, we can pass a numpy array that has negative strides.  Otherwise, an
+    exception will be thrown as Eigen will not be able to map the numpy array."""
+
+    counting_mat = np.arange(9.0, dtype=np.float32).reshape((3, 3))
+    counting_mat = counting_mat[::-1, ::-1]
+    second_row = counting_mat[1, :]
+    second_col = counting_mat[:, 1]
+    np.testing.assert_array_equal(m.double_row(second_row), 2.0 * second_row)
+    np.testing.assert_array_equal(m.double_col(second_row), 2.0 * second_row)
+    np.testing.assert_array_equal(m.double_complex(second_row), 2.0 * second_row)
+    np.testing.assert_array_equal(m.double_row(second_col), 2.0 * second_col)
+    np.testing.assert_array_equal(m.double_col(second_col), 2.0 * second_col)
+    np.testing.assert_array_equal(m.double_complex(second_col), 2.0 * second_col)
+
+    counting_3d = np.arange(27.0, dtype=np.float32).reshape((3, 3, 3))
+    counting_3d = counting_3d[::-1, ::-1, ::-1]
+    slices = [counting_3d[0, :, :], counting_3d[:, 0, :], counting_3d[:, :, 0]]
+    for ref_mat in slices:
+        np.testing.assert_array_equal(m.double_mat_cm(ref_mat), 2.0 * ref_mat)
+        np.testing.assert_array_equal(m.double_mat_rm(ref_mat), 2.0 * ref_mat)
+
+    # Mutator:
+    with pytest.raises(TypeError) as excinfo:
+        m.double_threer(second_row)
+    assert (
+        msg(excinfo.value)
+        == """
+        double_threer(): incompatible function arguments. The following argument types are supported:
+            1. (arg0: numpy.ndarray[numpy.float32[1, 3], flags.writeable]) -> None
+
+        Invoked with: """
+        + repr(np.array([5.0, 4.0, 3.0], dtype="float32"))
+    )
+
+    with pytest.raises(TypeError) as excinfo:
+        m.double_threec(second_col)
+    assert (
+        msg(excinfo.value)
+        == """
+        double_threec(): incompatible function arguments. The following argument types are supported:
+            1. (arg0: numpy.ndarray[numpy.float32[3, 1], flags.writeable]) -> None
+
+        Invoked with: """
+        + repr(np.array([7.0, 4.0, 1.0], dtype="float32"))
+    )
+
+
+def test_block_runtime_error_type_caster_eigen_ref_made_a_copy():
+    with pytest.raises(RuntimeError) as excinfo:
+        m.block(ref, 0, 0, 0, 0)
+    assert str(excinfo.value) == "type_caster for Eigen::Ref made a copy."
+
+
+def test_nonunit_stride_to_python():
+    assert np.all(m.diagonal(ref) == ref.diagonal())
+    assert np.all(m.diagonal_1(ref) == ref.diagonal(1))
+    for i in range(-5, 7):
+        assert np.all(m.diagonal_n(ref, i) == ref.diagonal(i)), f"m.diagonal_n({i})"
+
+    # Must be order="F", otherwise the type_caster will make a copy and
+    # m.block() will return a dangling reference (heap-use-after-free).
+    rof = np.asarray(ref, order="F")
+    assert np.all(m.block(rof, 2, 1, 3, 3) == rof[2:5, 1:4])
+    assert np.all(m.block(rof, 1, 4, 4, 2) == rof[1:, 4:])
+    assert np.all(m.block(rof, 1, 4, 3, 2) == rof[1:4, 4:])
+
+
+def test_eigen_ref_to_python():
+    chols = [m.cholesky1, m.cholesky2, m.cholesky3, m.cholesky4]
+    for i, chol in enumerate(chols, start=1):
+        mymat = chol(np.array([[1.0, 2, 4], [2, 13, 23], [4, 23, 77]]))
+        assert np.all(
+            mymat == np.array([[1, 0, 0], [2, 3, 0], [4, 5, 6]])
+        ), f"cholesky{i}"
+
+
+def assign_both(a1, a2, r, c, v):
+    a1[r, c] = v
+    a2[r, c] = v
+
+
+def array_copy_but_one(a, r, c, v):
+    z = np.array(a, copy=True)
+    z[r, c] = v
+    return z
+
+
+def test_eigen_return_references():
+    """Tests various ways of returning references and non-referencing copies"""
+
+    primary = np.ones((10, 10))
+    a = m.ReturnTester()
+    a_get1 = a.get()
+    assert not a_get1.flags.owndata
+    assert a_get1.flags.writeable
+    assign_both(a_get1, primary, 3, 3, 5)
+    a_get2 = a.get_ptr()
+    assert not a_get2.flags.owndata
+    assert a_get2.flags.writeable
+    assign_both(a_get1, primary, 2, 3, 6)
+
+    a_view1 = a.view()
+    assert not a_view1.flags.owndata
+    assert not a_view1.flags.writeable
+    with pytest.raises(ValueError):
+        a_view1[2, 3] = 4
+    a_view2 = a.view_ptr()
+    assert not a_view2.flags.owndata
+    assert not a_view2.flags.writeable
+    with pytest.raises(ValueError):
+        a_view2[2, 3] = 4
+
+    a_copy1 = a.copy_get()
+    assert a_copy1.flags.owndata
+    assert a_copy1.flags.writeable
+    np.testing.assert_array_equal(a_copy1, primary)
+    a_copy1[7, 7] = -44  # Shouldn't affect anything else
+    c1want = array_copy_but_one(primary, 7, 7, -44)
+    a_copy2 = a.copy_view()
+    assert a_copy2.flags.owndata
+    assert a_copy2.flags.writeable
+    np.testing.assert_array_equal(a_copy2, primary)
+    a_copy2[4, 4] = -22  # Shouldn't affect anything else
+    c2want = array_copy_but_one(primary, 4, 4, -22)
+
+    a_ref1 = a.ref()
+    assert not a_ref1.flags.owndata
+    assert a_ref1.flags.writeable
+    assign_both(a_ref1, primary, 1, 1, 15)
+    a_ref2 = a.ref_const()
+    assert not a_ref2.flags.owndata
+    assert not a_ref2.flags.writeable
+    with pytest.raises(ValueError):
+        a_ref2[5, 5] = 33
+    a_ref3 = a.ref_safe()
+    assert not a_ref3.flags.owndata
+    assert a_ref3.flags.writeable
+    assign_both(a_ref3, primary, 0, 7, 99)
+    a_ref4 = a.ref_const_safe()
+    assert not a_ref4.flags.owndata
+    assert not a_ref4.flags.writeable
+    with pytest.raises(ValueError):
+        a_ref4[7, 0] = 987654321
+
+    a_copy3 = a.copy_ref()
+    assert a_copy3.flags.owndata
+    assert a_copy3.flags.writeable
+    np.testing.assert_array_equal(a_copy3, primary)
+    a_copy3[8, 1] = 11
+    c3want = array_copy_but_one(primary, 8, 1, 11)
+    a_copy4 = a.copy_ref_const()
+    assert a_copy4.flags.owndata
+    assert a_copy4.flags.writeable
+    np.testing.assert_array_equal(a_copy4, primary)
+    a_copy4[8, 4] = 88
+    c4want = array_copy_but_one(primary, 8, 4, 88)
+
+    a_block1 = a.block(3, 3, 2, 2)
+    assert not a_block1.flags.owndata
+    assert a_block1.flags.writeable
+    a_block1[0, 0] = 55
+    primary[3, 3] = 55
+    a_block2 = a.block_safe(2, 2, 3, 2)
+    assert not a_block2.flags.owndata
+    assert a_block2.flags.writeable
+    a_block2[2, 1] = -123
+    primary[4, 3] = -123
+    a_block3 = a.block_const(6, 7, 4, 3)
+    assert not a_block3.flags.owndata
+    assert not a_block3.flags.writeable
+    with pytest.raises(ValueError):
+        a_block3[2, 2] = -44444
+
+    a_copy5 = a.copy_block(2, 2, 2, 3)
+    assert a_copy5.flags.owndata
+    assert a_copy5.flags.writeable
+    np.testing.assert_array_equal(a_copy5, primary[2:4, 2:5])
+    a_copy5[1, 1] = 777
+    c5want = array_copy_but_one(primary[2:4, 2:5], 1, 1, 777)
+
+    a_corn1 = a.corners()
+    assert not a_corn1.flags.owndata
+    assert a_corn1.flags.writeable
+    a_corn1 *= 50
+    a_corn1[1, 1] = 999
+    primary[0, 0] = 50
+    primary[0, 9] = 50
+    primary[9, 0] = 50
+    primary[9, 9] = 999
+    a_corn2 = a.corners_const()
+    assert not a_corn2.flags.owndata
+    assert not a_corn2.flags.writeable
+    with pytest.raises(ValueError):
+        a_corn2[1, 0] = 51
+
+    # All of the changes made all the way along should be visible everywhere
+    # now (except for the copies, of course)
+    np.testing.assert_array_equal(a_get1, primary)
+    np.testing.assert_array_equal(a_get2, primary)
+    np.testing.assert_array_equal(a_view1, primary)
+    np.testing.assert_array_equal(a_view2, primary)
+    np.testing.assert_array_equal(a_ref1, primary)
+    np.testing.assert_array_equal(a_ref2, primary)
+    np.testing.assert_array_equal(a_ref3, primary)
+    np.testing.assert_array_equal(a_ref4, primary)
+    np.testing.assert_array_equal(a_block1, primary[3:5, 3:5])
+    np.testing.assert_array_equal(a_block2, primary[2:5, 2:4])
+    np.testing.assert_array_equal(a_block3, primary[6:10, 7:10])
+    np.testing.assert_array_equal(
+        a_corn1, primary[0 :: primary.shape[0] - 1, 0 :: primary.shape[1] - 1]
+    )
+    np.testing.assert_array_equal(
+        a_corn2, primary[0 :: primary.shape[0] - 1, 0 :: primary.shape[1] - 1]
+    )
+
+    np.testing.assert_array_equal(a_copy1, c1want)
+    np.testing.assert_array_equal(a_copy2, c2want)
+    np.testing.assert_array_equal(a_copy3, c3want)
+    np.testing.assert_array_equal(a_copy4, c4want)
+    np.testing.assert_array_equal(a_copy5, c5want)
+
+
+def assert_keeps_alive(cl, method, *args):
+    cstats = ConstructorStats.get(cl)
+    start_with = cstats.alive()
+    a = cl()
+    assert cstats.alive() == start_with + 1
+    z = method(a, *args)
+    assert cstats.alive() == start_with + 1
+    del a
+    # Here's the keep alive in action:
+    assert cstats.alive() == start_with + 1
+    del z
+    # Keep alive should have expired:
+    assert cstats.alive() == start_with
+
+
+def test_eigen_keepalive():
+    a = m.ReturnTester()
+    cstats = ConstructorStats.get(m.ReturnTester)
+    assert cstats.alive() == 1
+    unsafe = [a.ref(), a.ref_const(), a.block(1, 2, 3, 4)]
+    copies = [
+        a.copy_get(),
+        a.copy_view(),
+        a.copy_ref(),
+        a.copy_ref_const(),
+        a.copy_block(4, 3, 2, 1),
+    ]
+    del a
+    assert cstats.alive() == 0
+    del unsafe
+    del copies
+
+    for meth in [
+        m.ReturnTester.get,
+        m.ReturnTester.get_ptr,
+        m.ReturnTester.view,
+        m.ReturnTester.view_ptr,
+        m.ReturnTester.ref_safe,
+        m.ReturnTester.ref_const_safe,
+        m.ReturnTester.corners,
+        m.ReturnTester.corners_const,
+    ]:
+        assert_keeps_alive(m.ReturnTester, meth)
+
+    for meth in [m.ReturnTester.block_safe, m.ReturnTester.block_const]:
+        assert_keeps_alive(m.ReturnTester, meth, 4, 3, 2, 1)
+
+
+def test_eigen_ref_mutators():
+    """Tests Eigen's ability to mutate numpy values"""
+
+    orig = np.array([[1.0, 2, 3], [4, 5, 6], [7, 8, 9]])
+    zr = np.array(orig)
+    zc = np.array(orig, order="F")
+    m.add_rm(zr, 1, 0, 100)
+    assert np.all(zr == np.array([[1.0, 2, 3], [104, 5, 6], [7, 8, 9]]))
+    m.add_cm(zc, 1, 0, 200)
+    assert np.all(zc == np.array([[1.0, 2, 3], [204, 5, 6], [7, 8, 9]]))
+
+    m.add_any(zr, 1, 0, 20)
+    assert np.all(zr == np.array([[1.0, 2, 3], [124, 5, 6], [7, 8, 9]]))
+    m.add_any(zc, 1, 0, 10)
+    assert np.all(zc == np.array([[1.0, 2, 3], [214, 5, 6], [7, 8, 9]]))
+
+    # Can't reference a col-major array with a row-major Ref, and vice versa:
+    with pytest.raises(TypeError):
+        m.add_rm(zc, 1, 0, 1)
+    with pytest.raises(TypeError):
+        m.add_cm(zr, 1, 0, 1)
+
+    # Overloads:
+    m.add1(zr, 1, 0, -100)
+    m.add2(zr, 1, 0, -20)
+    assert np.all(zr == orig)
+    m.add1(zc, 1, 0, -200)
+    m.add2(zc, 1, 0, -10)
+    assert np.all(zc == orig)
+
+    # a non-contiguous slice (this won't work on either the row- or
+    # column-contiguous refs, but should work for the any)
+    cornersr = zr[0::2, 0::2]
+    cornersc = zc[0::2, 0::2]
+
+    assert np.all(cornersr == np.array([[1.0, 3], [7, 9]]))
+    assert np.all(cornersc == np.array([[1.0, 3], [7, 9]]))
+
+    with pytest.raises(TypeError):
+        m.add_rm(cornersr, 0, 1, 25)
+    with pytest.raises(TypeError):
+        m.add_cm(cornersr, 0, 1, 25)
+    with pytest.raises(TypeError):
+        m.add_rm(cornersc, 0, 1, 25)
+    with pytest.raises(TypeError):
+        m.add_cm(cornersc, 0, 1, 25)
+    m.add_any(cornersr, 0, 1, 25)
+    m.add_any(cornersc, 0, 1, 44)
+    assert np.all(zr == np.array([[1.0, 2, 28], [4, 5, 6], [7, 8, 9]]))
+    assert np.all(zc == np.array([[1.0, 2, 47], [4, 5, 6], [7, 8, 9]]))
+
+    # You shouldn't be allowed to pass a non-writeable array to a mutating Eigen method:
+    zro = zr[0:4, 0:4]
+    zro.flags.writeable = False
+    with pytest.raises(TypeError):
+        m.add_rm(zro, 0, 0, 0)
+    with pytest.raises(TypeError):
+        m.add_any(zro, 0, 0, 0)
+    with pytest.raises(TypeError):
+        m.add1(zro, 0, 0, 0)
+    with pytest.raises(TypeError):
+        m.add2(zro, 0, 0, 0)
+
+    # integer array shouldn't be passable to a double-matrix-accepting mutating func:
+    zi = np.array([[1, 2], [3, 4]])
+    with pytest.raises(TypeError):
+        m.add_rm(zi)
+
+
+def test_numpy_ref_mutators():
+    """Tests numpy mutating Eigen matrices (for returned Eigen::Ref<...>s)"""
+
+    m.reset_refs()  # In case another test already changed it
+
+    zc = m.get_cm_ref()
+    zcro = m.get_cm_const_ref()
+    zr = m.get_rm_ref()
+    zrro = m.get_rm_const_ref()
+
+    assert [zc[1, 2], zcro[1, 2], zr[1, 2], zrro[1, 2]] == [23] * 4
+
+    assert not zc.flags.owndata
+    assert zc.flags.writeable
+    assert not zr.flags.owndata
+    assert zr.flags.writeable
+    assert not zcro.flags.owndata
+    assert not zcro.flags.writeable
+    assert not zrro.flags.owndata
+    assert not zrro.flags.writeable
+
+    zc[1, 2] = 99
+    expect = np.array([[11.0, 12, 13], [21, 22, 99], [31, 32, 33]])
+    # We should have just changed zc, of course, but also zcro and the original eigen matrix
+    assert np.all(zc == expect)
+    assert np.all(zcro == expect)
+    assert np.all(m.get_cm_ref() == expect)
+
+    zr[1, 2] = 99
+    assert np.all(zr == expect)
+    assert np.all(zrro == expect)
+    assert np.all(m.get_rm_ref() == expect)
+
+    # Make sure the readonly ones are numpy-readonly:
+    with pytest.raises(ValueError):
+        zcro[1, 2] = 6
+    with pytest.raises(ValueError):
+        zrro[1, 2] = 6
+
+    # We should be able to explicitly copy like this (and since we're copying,
+    # the const should drop away)
+    y1 = np.array(m.get_cm_const_ref())
+
+    assert y1.flags.owndata
+    assert y1.flags.writeable
+    # We should get copies of the eigen data, which was modified above:
+    assert y1[1, 2] == 99
+    y1[1, 2] += 12
+    assert y1[1, 2] == 111
+    assert zc[1, 2] == 99  # Make sure we aren't referencing the original
+
+
+def test_both_ref_mutators():
+    """Tests a complex chain of nested eigen/numpy references"""
+
+    m.reset_refs()  # In case another test already changed it
+
+    z = m.get_cm_ref()  # numpy -> eigen
+    z[0, 2] -= 3
+    z2 = m.incr_matrix(z, 1)  # numpy -> eigen -> numpy -> eigen
+    z2[1, 1] += 6
+    z3 = m.incr_matrix(z, 2)  # (numpy -> eigen)^3
+    z3[2, 2] += -5
+    z4 = m.incr_matrix(z, 3)  # (numpy -> eigen)^4
+    z4[1, 1] -= 1
+    z5 = m.incr_matrix(z, 4)  # (numpy -> eigen)^5
+    z5[0, 0] = 0
+    assert np.all(z == z2)
+    assert np.all(z == z3)
+    assert np.all(z == z4)
+    assert np.all(z == z5)
+    expect = np.array([[0.0, 22, 20], [31, 37, 33], [41, 42, 38]])
+    assert np.all(z == expect)
+
+    y = np.array(range(100), dtype="float64").reshape(10, 10)
+    y2 = m.incr_matrix_any(y, 10)  # np -> eigen -> np
+    y3 = m.incr_matrix_any(
+        y2[0::2, 0::2], -33
+    )  # np -> eigen -> np slice -> np -> eigen -> np
+    y4 = m.even_rows(y3)  # numpy -> eigen slice -> (... y3)
+    y5 = m.even_cols(y4)  # numpy -> eigen slice -> (... y4)
+    y6 = m.incr_matrix_any(y5, 1000)  # numpy -> eigen -> (... y5)
+
+    # Apply same mutations using just numpy:
+    yexpect = np.array(range(100), dtype="float64").reshape(10, 10)
+    yexpect += 10
+    yexpect[0::2, 0::2] -= 33
+    yexpect[0::4, 0::4] += 1000
+    assert np.all(y6 == yexpect[0::4, 0::4])
+    assert np.all(y5 == yexpect[0::4, 0::4])
+    assert np.all(y4 == yexpect[0::4, 0::2])
+    assert np.all(y3 == yexpect[0::2, 0::2])
+    assert np.all(y2 == yexpect)
+    assert np.all(y == yexpect)
+
+
+def test_nocopy_wrapper():
+    # get_elem requires a column-contiguous matrix reference, but should be
+    # callable with other types of matrix (via copying):
+    int_matrix_colmajor = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]], order="F")
+    dbl_matrix_colmajor = np.array(
+        int_matrix_colmajor, dtype="double", order="F", copy=True
+    )
+    int_matrix_rowmajor = np.array(int_matrix_colmajor, order="C", copy=True)
+    dbl_matrix_rowmajor = np.array(
+        int_matrix_rowmajor, dtype="double", order="C", copy=True
+    )
+
+    # All should be callable via get_elem:
+    assert m.get_elem(int_matrix_colmajor) == 8
+    assert m.get_elem(dbl_matrix_colmajor) == 8
+    assert m.get_elem(int_matrix_rowmajor) == 8
+    assert m.get_elem(dbl_matrix_rowmajor) == 8
+
+    # All but the second should fail with m.get_elem_nocopy:
+    with pytest.raises(TypeError) as excinfo:
+        m.get_elem_nocopy(int_matrix_colmajor)
+    assert "get_elem_nocopy(): incompatible function arguments." in str(excinfo.value)
+    assert ", flags.f_contiguous" in str(excinfo.value)
+    assert m.get_elem_nocopy(dbl_matrix_colmajor) == 8
+    with pytest.raises(TypeError) as excinfo:
+        m.get_elem_nocopy(int_matrix_rowmajor)
+    assert "get_elem_nocopy(): incompatible function arguments." in str(excinfo.value)
+    assert ", flags.f_contiguous" in str(excinfo.value)
+    with pytest.raises(TypeError) as excinfo:
+        m.get_elem_nocopy(dbl_matrix_rowmajor)
+    assert "get_elem_nocopy(): incompatible function arguments." in str(excinfo.value)
+    assert ", flags.f_contiguous" in str(excinfo.value)
+
+    # For the row-major test, we take a long matrix in row-major, so only the third is allowed:
+    with pytest.raises(TypeError) as excinfo:
+        m.get_elem_rm_nocopy(int_matrix_colmajor)
+    assert "get_elem_rm_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    )
+    assert ", flags.c_contiguous" in str(excinfo.value)
+    with pytest.raises(TypeError) as excinfo:
+        m.get_elem_rm_nocopy(dbl_matrix_colmajor)
+    assert "get_elem_rm_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    )
+    assert ", flags.c_contiguous" in str(excinfo.value)
+    assert m.get_elem_rm_nocopy(int_matrix_rowmajor) == 8
+    with pytest.raises(TypeError) as excinfo:
+        m.get_elem_rm_nocopy(dbl_matrix_rowmajor)
+    assert "get_elem_rm_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    )
+    assert ", flags.c_contiguous" in str(excinfo.value)
+
+
+def test_eigen_ref_life_support():
+    """Ensure the lifetime of temporary arrays created by the `Ref` caster
+
+    The `Ref` caster sometimes creates a copy which needs to stay alive. This needs to
+    happen both for directs casts (just the array) or indirectly (e.g. list of arrays).
+    """
+
+    a = np.full(shape=10, fill_value=8, dtype=np.int8)
+    assert m.get_elem_direct(a) == 8
+
+    list_of_a = [a]
+    assert m.get_elem_indirect(list_of_a) == 8
+
+
+def test_special_matrix_objects():
+    assert np.all(m.incr_diag(7) == np.diag([1.0, 2, 3, 4, 5, 6, 7]))
+
+    asymm = np.array([[1.0, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]])
+    symm_lower = np.array(asymm)
+    symm_upper = np.array(asymm)
+    for i in range(4):
+        for j in range(i + 1, 4):
+            symm_lower[i, j] = symm_lower[j, i]
+            symm_upper[j, i] = symm_upper[i, j]
+
+    assert np.all(m.symmetric_lower(asymm) == symm_lower)
+    assert np.all(m.symmetric_upper(asymm) == symm_upper)
+
+
+def test_dense_signature(doc):
+    assert (
+        doc(m.double_col)
+        == """
+        double_col(arg0: numpy.ndarray[numpy.float32[m, 1]]) -> numpy.ndarray[numpy.float32[m, 1]]
+    """
+    )
+    assert (
+        doc(m.double_row)
+        == """
+        double_row(arg0: numpy.ndarray[numpy.float32[1, n]]) -> numpy.ndarray[numpy.float32[1, n]]
+    """
+    )
+    assert doc(m.double_complex) == (
+        """
+        double_complex(arg0: numpy.ndarray[numpy.complex64[m, 1]])"""
+        """ -> numpy.ndarray[numpy.complex64[m, 1]]
+    """
+    )
+    assert doc(m.double_mat_rm) == (
+        """
+        double_mat_rm(arg0: numpy.ndarray[numpy.float32[m, n]])"""
+        """ -> numpy.ndarray[numpy.float32[m, n]]
+    """
+    )
+
+
+def test_named_arguments():
+    a = np.array([[1.0, 2], [3, 4], [5, 6]])
+    b = np.ones((2, 1))
+
+    assert np.all(m.matrix_multiply(a, b) == np.array([[3.0], [7], [11]]))
+    assert np.all(m.matrix_multiply(A=a, B=b) == np.array([[3.0], [7], [11]]))
+    assert np.all(m.matrix_multiply(B=b, A=a) == np.array([[3.0], [7], [11]]))
+
+    with pytest.raises(ValueError) as excinfo:
+        m.matrix_multiply(b, a)
+    assert str(excinfo.value) == "Nonconformable matrices!"
+
+    with pytest.raises(ValueError) as excinfo:
+        m.matrix_multiply(A=b, B=a)
+    assert str(excinfo.value) == "Nonconformable matrices!"
+
+    with pytest.raises(ValueError) as excinfo:
+        m.matrix_multiply(B=a, A=b)
+    assert str(excinfo.value) == "Nonconformable matrices!"
+
+
+def test_sparse():
+    pytest.importorskip("scipy")
+    assert_sparse_equal_ref(m.sparse_r())
+    assert_sparse_equal_ref(m.sparse_c())
+    assert_sparse_equal_ref(m.sparse_copy_r(m.sparse_r()))
+    assert_sparse_equal_ref(m.sparse_copy_c(m.sparse_c()))
+    assert_sparse_equal_ref(m.sparse_copy_r(m.sparse_c()))
+    assert_sparse_equal_ref(m.sparse_copy_c(m.sparse_r()))
+
+
+def test_sparse_signature(doc):
+    pytest.importorskip("scipy")
+    assert (
+        doc(m.sparse_copy_r)
+        == """
+        sparse_copy_r(arg0: scipy.sparse.csr_matrix[numpy.float32]) -> scipy.sparse.csr_matrix[numpy.float32]
+    """
+    )
+    assert (
+        doc(m.sparse_copy_c)
+        == """
+        sparse_copy_c(arg0: scipy.sparse.csc_matrix[numpy.float32]) -> scipy.sparse.csc_matrix[numpy.float32]
+    """
+    )
+
+
+def test_issue738():
+    """Ignore strides on a length-1 dimension (even if they would be incompatible length > 1)"""
+    assert np.all(m.iss738_f1(np.array([[1.0, 2, 3]])) == np.array([[1.0, 102, 203]]))
+    assert np.all(
+        m.iss738_f1(np.array([[1.0], [2], [3]])) == np.array([[1.0], [12], [23]])
+    )
+
+    assert np.all(m.iss738_f2(np.array([[1.0, 2, 3]])) == np.array([[1.0, 102, 203]]))
+    assert np.all(
+        m.iss738_f2(np.array([[1.0], [2], [3]])) == np.array([[1.0], [12], [23]])
+    )
+
+
+@pytest.mark.parametrize("func", [m.iss738_f1, m.iss738_f2])
+@pytest.mark.parametrize("sizes", [(0, 2), (2, 0)])
+def test_zero_length(func, sizes):
+    """Ignore strides on a length-0 dimension (even if they would be incompatible length > 1)"""
+    assert np.all(func(np.zeros(sizes)) == np.zeros(sizes))
+
+
+def test_issue1105():
+    """Issue 1105: 1xN or Nx1 input arrays weren't accepted for eigen
+    compile-time row vectors or column vector"""
+    assert m.iss1105_row(np.ones((1, 7)))
+    assert m.iss1105_col(np.ones((7, 1)))
+
+    # These should still fail (incompatible dimensions):
+    with pytest.raises(TypeError) as excinfo:
+        m.iss1105_row(np.ones((7, 1)))
+    assert "incompatible function arguments" in str(excinfo.value)
+    with pytest.raises(TypeError) as excinfo:
+        m.iss1105_col(np.ones((1, 7)))
+    assert "incompatible function arguments" in str(excinfo.value)
+
+
+def test_custom_operator_new():
+    """Using Eigen types as member variables requires a class-specific
+    operator new with proper alignment"""
+
+    o = m.CustomOperatorNew()
+    np.testing.assert_allclose(o.a, 0.0)
+    np.testing.assert_allclose(o.b.diagonal(), 1.0)
diff --git a/wrap/pybind11/tests/test_eigen_tensor.cpp b/wrap/pybind11/tests/test_eigen_tensor.cpp
new file mode 100644
index 000000000..503c69c7d
--- /dev/null
+++ b/wrap/pybind11/tests/test_eigen_tensor.cpp
@@ -0,0 +1,18 @@
+/*
+    tests/eigen_tensor.cpp -- automatic conversion of Eigen Tensor
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#define PYBIND11_TEST_EIGEN_TENSOR_NAMESPACE eigen_tensor
+
+#ifdef EIGEN_AVOID_STL_ARRAY
+#    undef EIGEN_AVOID_STL_ARRAY
+#endif
+
+#include "test_eigen_tensor.inl"
+
+#include "pybind11_tests.h"
+
+test_initializer egien_tensor("eigen_tensor", eigen_tensor_test::test_module);
diff --git a/wrap/pybind11/tests/test_eigen_tensor.inl b/wrap/pybind11/tests/test_eigen_tensor.inl
new file mode 100644
index 000000000..d864ce737
--- /dev/null
+++ b/wrap/pybind11/tests/test_eigen_tensor.inl
@@ -0,0 +1,333 @@
+/*
+    tests/eigen_tensor.cpp -- automatic conversion of Eigen Tensor
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#include <pybind11/eigen/tensor.h>
+
+PYBIND11_NAMESPACE_BEGIN(eigen_tensor_test)
+
+namespace py = pybind11;
+
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
+template <typename M>
+void reset_tensor(M &x) {
+    for (int i = 0; i < x.dimension(0); i++) {
+        for (int j = 0; j < x.dimension(1); j++) {
+            for (int k = 0; k < x.dimension(2); k++) {
+                x(i, j, k) = i * (5 * 2) + j * 2 + k;
+            }
+        }
+    }
+}
+
+template <typename M>
+bool check_tensor(M &x) {
+    for (int i = 0; i < x.dimension(0); i++) {
+        for (int j = 0; j < x.dimension(1); j++) {
+            for (int k = 0; k < x.dimension(2); k++) {
+                if (x(i, j, k) != (i * (5 * 2) + j * 2 + k)) {
+                    return false;
+                }
+            }
+        }
+    }
+    return true;
+}
+
+template <int Options>
+Eigen::Tensor<double, 3, Options> &get_tensor() {
+    static Eigen::Tensor<double, 3, Options> *x;
+
+    if (!x) {
+        x = new Eigen::Tensor<double, 3, Options>(3, 5, 2);
+        reset_tensor(*x);
+    }
+
+    return *x;
+}
+
+template <int Options>
+Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> &get_tensor_map() {
+    static Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> *x;
+
+    if (!x) {
+        x = new Eigen::TensorMap<Eigen::Tensor<double, 3, Options>>(get_tensor<Options>());
+    }
+
+    return *x;
+}
+
+template <int Options>
+Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options> &get_fixed_tensor() {
+    static Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options> *x;
+
+    if (!x) {
+        Eigen::aligned_allocator<Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options>>
+            allocator;
+        x = new (allocator.allocate(1))
+            Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options>();
+        reset_tensor(*x);
+    }
+
+    return *x;
+}
+
+template <int Options>
+const Eigen::Tensor<double, 3, Options> &get_const_tensor() {
+    return get_tensor<Options>();
+}
+
+template <int Options>
+struct CustomExample {
+    CustomExample() : member(get_tensor<Options>()), view_member(member) {}
+
+    Eigen::Tensor<double, 3, Options> member;
+    Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> view_member;
+};
+
+template <int Options>
+void init_tensor_module(pybind11::module &m) {
+    const char *needed_options = "";
+    if (Options == Eigen::ColMajor) {
+        needed_options = "F";
+    } else {
+        needed_options = "C";
+    }
+    m.attr("needed_options") = needed_options;
+
+    m.def("setup", []() {
+        reset_tensor(get_tensor<Options>());
+        reset_tensor(get_fixed_tensor<Options>());
+    });
+
+    m.def("is_ok", []() {
+        return check_tensor(get_tensor<Options>()) && check_tensor(get_fixed_tensor<Options>());
+    });
+
+    py::class_<CustomExample<Options>>(m, "CustomExample", py::module_local())
+        .def(py::init<>())
+        .def_readonly(
+            "member", &CustomExample<Options>::member, py::return_value_policy::reference_internal)
+        .def_readonly("member_view",
+                      &CustomExample<Options>::view_member,
+                      py::return_value_policy::reference_internal);
+
+    m.def(
+        "copy_fixed_tensor",
+        []() { return &get_fixed_tensor<Options>(); },
+        py::return_value_policy::copy);
+
+    m.def(
+        "copy_tensor", []() { return &get_tensor<Options>(); }, py::return_value_policy::copy);
+
+    m.def(
+        "copy_const_tensor",
+        []() { return &get_const_tensor<Options>(); },
+        py::return_value_policy::copy);
+
+    m.def(
+        "move_fixed_tensor_copy",
+        []() -> Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options> {
+            return get_fixed_tensor<Options>();
+        },
+        py::return_value_policy::move);
+
+    m.def(
+        "move_tensor_copy",
+        []() -> Eigen::Tensor<double, 3, Options> { return get_tensor<Options>(); },
+        py::return_value_policy::move);
+
+    m.def(
+        "move_const_tensor",
+        []() -> const Eigen::Tensor<double, 3, Options> & { return get_const_tensor<Options>(); },
+        py::return_value_policy::move);
+
+    m.def(
+        "take_fixed_tensor",
+
+        []() {
+            Eigen::aligned_allocator<
+                Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options>>
+                allocator;
+            return new (allocator.allocate(1))
+                Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options>(
+                    get_fixed_tensor<Options>());
+        },
+        py::return_value_policy::take_ownership);
+
+    m.def(
+        "take_tensor",
+        []() { return new Eigen::Tensor<double, 3, Options>(get_tensor<Options>()); },
+        py::return_value_policy::take_ownership);
+
+    m.def(
+        "take_const_tensor",
+        []() -> const Eigen::Tensor<double, 3, Options> * {
+            return new Eigen::Tensor<double, 3, Options>(get_tensor<Options>());
+        },
+        py::return_value_policy::take_ownership);
+
+    m.def(
+        "take_view_tensor",
+        []() -> const Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> * {
+            return new Eigen::TensorMap<Eigen::Tensor<double, 3, Options>>(get_tensor<Options>());
+        },
+        py::return_value_policy::take_ownership);
+
+    m.def(
+        "reference_tensor",
+        []() { return &get_tensor<Options>(); },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_tensor_v2",
+        []() -> Eigen::Tensor<double, 3, Options> & { return get_tensor<Options>(); },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_tensor_internal",
+        []() { return &get_tensor<Options>(); },
+        py::return_value_policy::reference_internal);
+
+    m.def(
+        "reference_fixed_tensor",
+        []() { return &get_tensor<Options>(); },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_const_tensor",
+        []() { return &get_const_tensor<Options>(); },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_const_tensor_v2",
+        []() -> const Eigen::Tensor<double, 3, Options> & { return get_const_tensor<Options>(); },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_tensor",
+        []() -> Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> {
+            return get_tensor_map<Options>();
+        },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_tensor_v2",
+        // NOLINTNEXTLINE(readability-const-return-type)
+        []() -> const Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> {
+            return get_tensor_map<Options>(); // NOLINT(readability-const-return-type)
+        },                                    // NOLINT(readability-const-return-type)
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_tensor_v3",
+        []() -> Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> * {
+            return &get_tensor_map<Options>();
+        },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_tensor_v4",
+        []() -> const Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> * {
+            return &get_tensor_map<Options>();
+        },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_tensor_v5",
+        []() -> Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> & {
+            return get_tensor_map<Options>();
+        },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_tensor_v6",
+        []() -> const Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> & {
+            return get_tensor_map<Options>();
+        },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_fixed_tensor",
+        []() {
+            return Eigen::TensorMap<
+                Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options>>(
+                get_fixed_tensor<Options>());
+        },
+        py::return_value_policy::reference);
+
+    m.def("round_trip_tensor",
+          [](const Eigen::Tensor<double, 3, Options> &tensor) { return tensor; });
+
+    m.def(
+        "round_trip_tensor_noconvert",
+        [](const Eigen::Tensor<double, 3, Options> &tensor) { return tensor; },
+        py::arg("tensor").noconvert());
+
+    m.def("round_trip_tensor2",
+          [](const Eigen::Tensor<int32_t, 3, Options> &tensor) { return tensor; });
+
+    m.def("round_trip_fixed_tensor",
+          [](const Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options> &tensor) {
+              return tensor;
+          });
+
+    m.def(
+        "round_trip_view_tensor",
+        [](Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> view) { return view; },
+        py::return_value_policy::reference);
+
+    m.def(
+        "round_trip_view_tensor_ref",
+        [](Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> &view) { return view; },
+        py::return_value_policy::reference);
+
+    m.def(
+        "round_trip_view_tensor_ptr",
+        [](Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> *view) { return view; },
+        py::return_value_policy::reference);
+
+    m.def(
+        "round_trip_aligned_view_tensor",
+        [](Eigen::TensorMap<Eigen::Tensor<double, 3, Options>, Eigen::Aligned> view) {
+            return view;
+        },
+        py::return_value_policy::reference);
+
+    m.def(
+        "round_trip_const_view_tensor",
+        [](Eigen::TensorMap<const Eigen::Tensor<double, 3, Options>> view) {
+            return Eigen::Tensor<double, 3, Options>(view);
+        },
+        py::return_value_policy::move);
+
+    m.def(
+        "round_trip_rank_0",
+        [](const Eigen::Tensor<double, 0, Options> &tensor) { return tensor; },
+        py::return_value_policy::move);
+
+    m.def(
+        "round_trip_rank_0_noconvert",
+        [](const Eigen::Tensor<double, 0, Options> &tensor) { return tensor; },
+        py::arg("tensor").noconvert(),
+        py::return_value_policy::move);
+
+    m.def(
+        "round_trip_rank_0_view",
+        [](Eigen::TensorMap<Eigen::Tensor<double, 0, Options>> &tensor) { return tensor; },
+        py::return_value_policy::reference);
+}
+
+void test_module(py::module_ &m) {
+    auto f_style = m.def_submodule("f_style");
+    auto c_style = m.def_submodule("c_style");
+
+    init_tensor_module<Eigen::ColMajor>(f_style);
+    init_tensor_module<Eigen::RowMajor>(c_style);
+}
+
+PYBIND11_NAMESPACE_END(eigen_tensor_test)
diff --git a/wrap/pybind11/tests/test_eigen_tensor.py b/wrap/pybind11/tests/test_eigen_tensor.py
new file mode 100644
index 000000000..3e7ee6b7f
--- /dev/null
+++ b/wrap/pybind11/tests/test_eigen_tensor.py
@@ -0,0 +1,288 @@
+import sys
+
+import pytest
+
+np = pytest.importorskip("numpy")
+eigen_tensor = pytest.importorskip("pybind11_tests.eigen_tensor")
+submodules = [eigen_tensor.c_style, eigen_tensor.f_style]
+try:
+    import eigen_tensor_avoid_stl_array as avoid
+
+    submodules += [avoid.c_style, avoid.f_style]
+except ImportError as e:
+    # Ensure config, build, toolchain, etc. issues are not masked here:
+    msg = (
+        "import eigen_tensor_avoid_stl_array FAILED, while "
+        "import pybind11_tests.eigen_tensor succeeded. "
+        "Please ensure that "
+        "test_eigen_tensor.cpp & "
+        "eigen_tensor_avoid_stl_array.cpp "
+        "are built together (or both are not built if Eigen is not available)."
+    )
+    raise RuntimeError(msg) from e
+
+tensor_ref = np.empty((3, 5, 2), dtype=np.int64)
+
+for i in range(tensor_ref.shape[0]):
+    for j in range(tensor_ref.shape[1]):
+        for k in range(tensor_ref.shape[2]):
+            tensor_ref[i, j, k] = i * (5 * 2) + j * 2 + k
+
+indices = (2, 3, 1)
+
+
+@pytest.fixture(autouse=True)
+def cleanup():
+    for module in submodules:
+        module.setup()
+
+    yield
+
+    for module in submodules:
+        assert module.is_ok()
+
+
+def test_import_avoid_stl_array():
+    pytest.importorskip("eigen_tensor_avoid_stl_array")
+    assert len(submodules) == 4
+
+
+def assert_equal_tensor_ref(mat, writeable=True, modified=None):
+    assert mat.flags.writeable == writeable
+
+    copy = np.array(tensor_ref)
+    if modified is not None:
+        copy[indices] = modified
+
+    np.testing.assert_array_equal(mat, copy)
+
+
+@pytest.mark.parametrize("m", submodules)
+@pytest.mark.parametrize("member_name", ["member", "member_view"])
+def test_reference_internal(m, member_name):
+    if not hasattr(sys, "getrefcount"):
+        pytest.skip("No reference counting")
+    foo = m.CustomExample()
+    counts = sys.getrefcount(foo)
+    mem = getattr(foo, member_name)
+    assert_equal_tensor_ref(mem, writeable=False)
+    new_counts = sys.getrefcount(foo)
+    assert new_counts == counts + 1
+    assert_equal_tensor_ref(mem, writeable=False)
+    del mem
+    assert sys.getrefcount(foo) == counts
+
+
+assert_equal_funcs = [
+    "copy_tensor",
+    "copy_fixed_tensor",
+    "copy_const_tensor",
+    "move_tensor_copy",
+    "move_fixed_tensor_copy",
+    "take_tensor",
+    "take_fixed_tensor",
+    "reference_tensor",
+    "reference_tensor_v2",
+    "reference_fixed_tensor",
+    "reference_view_of_tensor",
+    "reference_view_of_tensor_v3",
+    "reference_view_of_tensor_v5",
+    "reference_view_of_fixed_tensor",
+]
+
+assert_equal_const_funcs = [
+    "reference_view_of_tensor_v2",
+    "reference_view_of_tensor_v4",
+    "reference_view_of_tensor_v6",
+    "reference_const_tensor",
+    "reference_const_tensor_v2",
+]
+
+
+@pytest.mark.parametrize("m", submodules)
+@pytest.mark.parametrize("func_name", assert_equal_funcs + assert_equal_const_funcs)
+def test_convert_tensor_to_py(m, func_name):
+    writeable = func_name in assert_equal_funcs
+    assert_equal_tensor_ref(getattr(m, func_name)(), writeable=writeable)
+
+
+@pytest.mark.parametrize("m", submodules)
+def test_bad_cpp_to_python_casts(m):
+    with pytest.raises(
+        RuntimeError, match="Cannot use reference internal when there is no parent"
+    ):
+        m.reference_tensor_internal()
+
+    with pytest.raises(RuntimeError, match="Cannot move from a constant reference"):
+        m.move_const_tensor()
+
+    with pytest.raises(
+        RuntimeError, match="Cannot take ownership of a const reference"
+    ):
+        m.take_const_tensor()
+
+    with pytest.raises(
+        RuntimeError,
+        match="Invalid return_value_policy for Eigen Map type, must be either reference or reference_internal",
+    ):
+        m.take_view_tensor()
+
+
+@pytest.mark.parametrize("m", submodules)
+def test_bad_python_to_cpp_casts(m):
+    with pytest.raises(
+        TypeError, match=r"^round_trip_tensor\(\): incompatible function arguments"
+    ):
+        m.round_trip_tensor(np.zeros((2, 3)))
+
+    with pytest.raises(TypeError, match=r"^Cannot cast array data from dtype"):
+        m.round_trip_tensor(np.zeros(dtype=np.str_, shape=(2, 3, 1)))
+
+    with pytest.raises(
+        TypeError,
+        match=r"^round_trip_tensor_noconvert\(\): incompatible function arguments",
+    ):
+        m.round_trip_tensor_noconvert(tensor_ref)
+
+    assert_equal_tensor_ref(
+        m.round_trip_tensor_noconvert(tensor_ref.astype(np.float64))
+    )
+
+    bad_options = "C" if m.needed_options == "F" else "F"
+    # Shape, dtype and the order need to be correct for a TensorMap cast
+    with pytest.raises(
+        TypeError, match=r"^round_trip_view_tensor\(\): incompatible function arguments"
+    ):
+        m.round_trip_view_tensor(
+            np.zeros((3, 5, 2), dtype=np.float64, order=bad_options)
+        )
+
+    with pytest.raises(
+        TypeError, match=r"^round_trip_view_tensor\(\): incompatible function arguments"
+    ):
+        m.round_trip_view_tensor(
+            np.zeros((3, 5, 2), dtype=np.float32, order=m.needed_options)
+        )
+
+    with pytest.raises(
+        TypeError, match=r"^round_trip_view_tensor\(\): incompatible function arguments"
+    ):
+        m.round_trip_view_tensor(
+            np.zeros((3, 5), dtype=np.float64, order=m.needed_options)
+        )
+
+    temp = np.zeros((3, 5, 2), dtype=np.float64, order=m.needed_options)
+    with pytest.raises(
+        TypeError, match=r"^round_trip_view_tensor\(\): incompatible function arguments"
+    ):
+        m.round_trip_view_tensor(
+            temp[:, ::-1, :],
+        )
+
+    temp = np.zeros((3, 5, 2), dtype=np.float64, order=m.needed_options)
+    temp.setflags(write=False)
+    with pytest.raises(
+        TypeError, match=r"^round_trip_view_tensor\(\): incompatible function arguments"
+    ):
+        m.round_trip_view_tensor(temp)
+
+
+@pytest.mark.parametrize("m", submodules)
+def test_references_actually_refer(m):
+    a = m.reference_tensor()
+    temp = a[indices]
+    a[indices] = 100
+    assert_equal_tensor_ref(m.copy_const_tensor(), modified=100)
+    a[indices] = temp
+    assert_equal_tensor_ref(m.copy_const_tensor())
+
+    a = m.reference_view_of_tensor()
+    a[indices] = 100
+    assert_equal_tensor_ref(m.copy_const_tensor(), modified=100)
+    a[indices] = temp
+    assert_equal_tensor_ref(m.copy_const_tensor())
+
+
+@pytest.mark.parametrize("m", submodules)
+def test_round_trip(m):
+    assert_equal_tensor_ref(m.round_trip_tensor(tensor_ref))
+
+    with pytest.raises(TypeError, match="^Cannot cast array data from"):
+        assert_equal_tensor_ref(m.round_trip_tensor2(tensor_ref))
+
+    assert_equal_tensor_ref(m.round_trip_tensor2(np.array(tensor_ref, dtype=np.int32)))
+    assert_equal_tensor_ref(m.round_trip_fixed_tensor(tensor_ref))
+    assert_equal_tensor_ref(m.round_trip_aligned_view_tensor(m.reference_tensor()))
+
+    copy = np.array(tensor_ref, dtype=np.float64, order=m.needed_options)
+    assert_equal_tensor_ref(m.round_trip_view_tensor(copy))
+    assert_equal_tensor_ref(m.round_trip_view_tensor_ref(copy))
+    assert_equal_tensor_ref(m.round_trip_view_tensor_ptr(copy))
+    copy.setflags(write=False)
+    assert_equal_tensor_ref(m.round_trip_const_view_tensor(copy))
+
+    np.testing.assert_array_equal(
+        tensor_ref[:, ::-1, :], m.round_trip_tensor(tensor_ref[:, ::-1, :])
+    )
+
+    assert m.round_trip_rank_0(np.float64(3.5)) == 3.5
+    assert m.round_trip_rank_0(3.5) == 3.5
+
+    with pytest.raises(
+        TypeError,
+        match=r"^round_trip_rank_0_noconvert\(\): incompatible function arguments",
+    ):
+        m.round_trip_rank_0_noconvert(np.float64(3.5))
+
+    with pytest.raises(
+        TypeError,
+        match=r"^round_trip_rank_0_noconvert\(\): incompatible function arguments",
+    ):
+        m.round_trip_rank_0_noconvert(3.5)
+
+    with pytest.raises(
+        TypeError, match=r"^round_trip_rank_0_view\(\): incompatible function arguments"
+    ):
+        m.round_trip_rank_0_view(np.float64(3.5))
+
+    with pytest.raises(
+        TypeError, match=r"^round_trip_rank_0_view\(\): incompatible function arguments"
+    ):
+        m.round_trip_rank_0_view(3.5)
+
+
+@pytest.mark.parametrize("m", submodules)
+def test_round_trip_references_actually_refer(m):
+    # Need to create a copy that matches the type on the C side
+    copy = np.array(tensor_ref, dtype=np.float64, order=m.needed_options)
+    a = m.round_trip_view_tensor(copy)
+    temp = a[indices]
+    a[indices] = 100
+    assert_equal_tensor_ref(copy, modified=100)
+    a[indices] = temp
+    assert_equal_tensor_ref(copy)
+
+
+@pytest.mark.parametrize("m", submodules)
+def test_doc_string(m, doc):
+    assert (
+        doc(m.copy_tensor) == "copy_tensor() -> numpy.ndarray[numpy.float64[?, ?, ?]]"
+    )
+    assert (
+        doc(m.copy_fixed_tensor)
+        == "copy_fixed_tensor() -> numpy.ndarray[numpy.float64[3, 5, 2]]"
+    )
+    assert (
+        doc(m.reference_const_tensor)
+        == "reference_const_tensor() -> numpy.ndarray[numpy.float64[?, ?, ?]]"
+    )
+
+    order_flag = f"flags.{m.needed_options.lower()}_contiguous"
+    assert doc(m.round_trip_view_tensor) == (
+        f"round_trip_view_tensor(arg0: numpy.ndarray[numpy.float64[?, ?, ?], flags.writeable, {order_flag}])"
+        f" -> numpy.ndarray[numpy.float64[?, ?, ?], flags.writeable, {order_flag}]"
+    )
+    assert doc(m.round_trip_const_view_tensor) == (
+        f"round_trip_const_view_tensor(arg0: numpy.ndarray[numpy.float64[?, ?, ?], {order_flag}])"
+        " -> numpy.ndarray[numpy.float64[?, ?, ?]]"
+    )
diff --git a/wrap/pybind11/tests/test_embed/catch.cpp b/wrap/pybind11/tests/test_embed/catch.cpp
index 96d2e3f92..558a7a35e 100644
--- a/wrap/pybind11/tests/test_embed/catch.cpp
+++ b/wrap/pybind11/tests/test_embed/catch.cpp
@@ -3,11 +3,9 @@
 
 #include <pybind11/embed.h>
 
-#ifdef _MSC_VER
 // Silence MSVC C++17 deprecation warning from Catch regarding std::uncaught_exceptions (up to
 // catch 2.0.1; this should be fixed in the next catch release after 2.0.1).
-#    pragma warning(disable : 4996)
-#endif
+PYBIND11_WARNING_DISABLE_MSVC(4996)
 
 // Catch uses _ internally, which breaks gettext style defines
 #ifdef _
@@ -20,7 +18,25 @@
 namespace py = pybind11;
 
 int main(int argc, char *argv[]) {
+    // Setup for TEST_CASE in test_interpreter.cpp, tagging on a large random number:
+    std::string updated_pythonpath("pybind11_test_embed_PYTHONPATH_2099743835476552");
+    const char *preexisting_pythonpath = getenv("PYTHONPATH");
+    if (preexisting_pythonpath != nullptr) {
+#if defined(_WIN32)
+        updated_pythonpath += ';';
+#else
+        updated_pythonpath += ':';
+#endif
+        updated_pythonpath += preexisting_pythonpath;
+    }
+#if defined(_WIN32)
+    _putenv_s("PYTHONPATH", updated_pythonpath.c_str());
+#else
+    setenv("PYTHONPATH", updated_pythonpath.c_str(), /*replace=*/1);
+#endif
+
     py::scoped_interpreter guard{};
+
     auto result = Catch::Session().run(argc, argv);
 
     return result < 0xff ? result : 0xff;
diff --git a/wrap/pybind11/tests/test_embed/test_interpreter.cpp b/wrap/pybind11/tests/test_embed/test_interpreter.cpp
index 1c45457a0..c6c8a22d9 100644
--- a/wrap/pybind11/tests/test_embed/test_interpreter.cpp
+++ b/wrap/pybind11/tests/test_embed/test_interpreter.cpp
@@ -1,10 +1,8 @@
 #include <pybind11/embed.h>
 
-#ifdef _MSC_VER
 // Silence MSVC C++17 deprecation warning from Catch regarding std::uncaught_exceptions (up to
 // catch 2.0.1; this should be fixed in the next catch release after 2.0.1).
-#    pragma warning(disable : 4996)
-#endif
+PYBIND11_WARNING_DISABLE_MSVC(4996)
 
 #include <catch.hpp>
 #include <cstdlib>
@@ -16,6 +14,11 @@
 namespace py = pybind11;
 using namespace py::literals;
 
+size_t get_sys_path_size() {
+    auto sys_path = py::module::import("sys").attr("path");
+    return py::len(sys_path);
+}
+
 class Widget {
 public:
     explicit Widget(std::string message) : message(std::move(message)) {}
@@ -75,6 +78,13 @@ PYBIND11_EMBEDDED_MODULE(throw_error_already_set, ) {
     d["missing"].cast<py::object>();
 }
 
+TEST_CASE("PYTHONPATH is used to update sys.path") {
+    // The setup for this TEST_CASE is in catch.cpp!
+    auto sys_path = py::str(py::module_::import("sys").attr("path")).cast<std::string>();
+    REQUIRE_THAT(sys_path,
+                 Catch::Matchers::Contains("pybind11_test_embed_PYTHONPATH_2099743835476552"));
+}
+
 TEST_CASE("Pass classes and data between modules defined in C++ and Python") {
     auto module_ = py::module_::import("test_interpreter");
     REQUIRE(py::hasattr(module_, "DerivedWidget"));
@@ -161,10 +171,94 @@ TEST_CASE("There can be only one interpreter") {
     py::initialize_interpreter();
 }
 
-bool has_pybind11_internals_builtin() {
-    auto builtins = py::handle(PyEval_GetBuiltins());
-    return builtins.contains(PYBIND11_INTERNALS_ID);
-};
+#if PY_VERSION_HEX >= PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX
+TEST_CASE("Custom PyConfig") {
+    py::finalize_interpreter();
+    PyConfig config;
+    PyConfig_InitPythonConfig(&config);
+    REQUIRE_NOTHROW(py::scoped_interpreter{&config});
+    {
+        py::scoped_interpreter p{&config};
+        REQUIRE(py::module_::import("widget_module").attr("add")(1, 41).cast<int>() == 42);
+    }
+    py::initialize_interpreter();
+}
+
+TEST_CASE("scoped_interpreter with PyConfig_InitIsolatedConfig and argv") {
+    py::finalize_interpreter();
+    {
+        PyConfig config;
+        PyConfig_InitIsolatedConfig(&config);
+        char *argv[] = {strdup("a.out")};
+        py::scoped_interpreter argv_scope{&config, 1, argv};
+        std::free(argv[0]);
+        auto module = py::module::import("test_interpreter");
+        auto py_widget = module.attr("DerivedWidget")("The question");
+        const auto &cpp_widget = py_widget.cast<const Widget &>();
+        REQUIRE(cpp_widget.argv0() == "a.out");
+    }
+    py::initialize_interpreter();
+}
+
+TEST_CASE("scoped_interpreter with PyConfig_InitPythonConfig and argv") {
+    py::finalize_interpreter();
+    {
+        PyConfig config;
+        PyConfig_InitPythonConfig(&config);
+
+        // `initialize_interpreter() overrides the default value for config.parse_argv (`1`) by
+        // changing it to `0`. This test exercises `scoped_interpreter` with the default config.
+        char *argv[] = {strdup("a.out"), strdup("arg1")};
+        py::scoped_interpreter argv_scope(&config, 2, argv);
+        std::free(argv[0]);
+        std::free(argv[1]);
+        auto module = py::module::import("test_interpreter");
+        auto py_widget = module.attr("DerivedWidget")("The question");
+        const auto &cpp_widget = py_widget.cast<const Widget &>();
+        REQUIRE(cpp_widget.argv0() == "arg1");
+    }
+    py::initialize_interpreter();
+}
+#endif
+
+TEST_CASE("Add program dir to path pre-PyConfig") {
+    py::finalize_interpreter();
+    size_t path_size_add_program_dir_to_path_false = 0;
+    {
+        py::scoped_interpreter scoped_interp{true, 0, nullptr, false};
+        path_size_add_program_dir_to_path_false = get_sys_path_size();
+    }
+    {
+        py::scoped_interpreter scoped_interp{};
+        REQUIRE(get_sys_path_size() == path_size_add_program_dir_to_path_false + 1);
+    }
+    py::initialize_interpreter();
+}
+
+#if PY_VERSION_HEX >= PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX
+TEST_CASE("Add program dir to path using PyConfig") {
+    py::finalize_interpreter();
+    size_t path_size_add_program_dir_to_path_false = 0;
+    {
+        PyConfig config;
+        PyConfig_InitPythonConfig(&config);
+        py::scoped_interpreter scoped_interp{&config, 0, nullptr, false};
+        path_size_add_program_dir_to_path_false = get_sys_path_size();
+    }
+    {
+        PyConfig config;
+        PyConfig_InitPythonConfig(&config);
+        py::scoped_interpreter scoped_interp{&config};
+        REQUIRE(get_sys_path_size() == path_size_add_program_dir_to_path_false + 1);
+    }
+    py::initialize_interpreter();
+}
+#endif
+
+bool has_state_dict_internals_obj() {
+    return bool(
+        py::detail::get_internals_obj_from_state_dict(py::detail::get_python_state_dict()));
+}
 
 bool has_pybind11_internals_static() {
     auto **&ipp = py::detail::get_internals_pp();
@@ -174,7 +268,7 @@ bool has_pybind11_internals_static() {
 TEST_CASE("Restart the interpreter") {
     // Verify pre-restart state.
     REQUIRE(py::module_::import("widget_module").attr("add")(1, 2).cast<int>() == 3);
-    REQUIRE(has_pybind11_internals_builtin());
+    REQUIRE(has_state_dict_internals_obj());
     REQUIRE(has_pybind11_internals_static());
     REQUIRE(py::module_::import("external_module").attr("A")(123).attr("value").cast<int>()
             == 123);
@@ -191,10 +285,10 @@ TEST_CASE("Restart the interpreter") {
     REQUIRE(Py_IsInitialized() == 1);
 
     // Internals are deleted after a restart.
-    REQUIRE_FALSE(has_pybind11_internals_builtin());
+    REQUIRE_FALSE(has_state_dict_internals_obj());
     REQUIRE_FALSE(has_pybind11_internals_static());
     pybind11::detail::get_internals();
-    REQUIRE(has_pybind11_internals_builtin());
+    REQUIRE(has_state_dict_internals_obj());
     REQUIRE(has_pybind11_internals_static());
     REQUIRE(reinterpret_cast<uintptr_t>(*py::detail::get_internals_pp())
             == py::module_::import("external_module").attr("internals_at")().cast<uintptr_t>());
@@ -209,13 +303,13 @@ TEST_CASE("Restart the interpreter") {
               py::detail::get_internals();
               *static_cast<bool *>(ran) = true;
           });
-    REQUIRE_FALSE(has_pybind11_internals_builtin());
+    REQUIRE_FALSE(has_state_dict_internals_obj());
     REQUIRE_FALSE(has_pybind11_internals_static());
     REQUIRE_FALSE(ran);
     py::finalize_interpreter();
     REQUIRE(ran);
     py::initialize_interpreter();
-    REQUIRE_FALSE(has_pybind11_internals_builtin());
+    REQUIRE_FALSE(has_state_dict_internals_obj());
     REQUIRE_FALSE(has_pybind11_internals_static());
 
     // C++ modules can be reloaded.
@@ -237,7 +331,7 @@ TEST_CASE("Subinterpreter") {
 
         REQUIRE(m.attr("add")(1, 2).cast<int>() == 3);
     }
-    REQUIRE(has_pybind11_internals_builtin());
+    REQUIRE(has_state_dict_internals_obj());
     REQUIRE(has_pybind11_internals_static());
 
     /// Create and switch to a subinterpreter.
@@ -247,7 +341,7 @@ TEST_CASE("Subinterpreter") {
     // Subinterpreters get their own copy of builtins. detail::get_internals() still
     // works by returning from the static variable, i.e. all interpreters share a single
     // global pybind11::internals;
-    REQUIRE_FALSE(has_pybind11_internals_builtin());
+    REQUIRE_FALSE(has_state_dict_internals_obj());
     REQUIRE(has_pybind11_internals_static());
 
     // Modules tags should be gone.
@@ -286,7 +380,6 @@ TEST_CASE("Threads") {
 
     {
         py::gil_scoped_release gil_release{};
-        REQUIRE(has_pybind11_internals_static());
 
         auto threads = std::vector<std::thread>();
         for (auto i = 0; i < num_threads; ++i) {
diff --git a/wrap/pybind11/tests/test_enum.py b/wrap/pybind11/tests/test_enum.py
index f14a72398..4e85d29c3 100644
--- a/wrap/pybind11/tests/test_enum.py
+++ b/wrap/pybind11/tests/test_enum.py
@@ -1,3 +1,5 @@
+# ruff: noqa: SIM201 SIM300 SIM202
+
 import pytest
 
 from pybind11_tests import enums as m
diff --git a/wrap/pybind11/tests/test_exceptions.cpp b/wrap/pybind11/tests/test_exceptions.cpp
index 3ec999d1d..854c7e6f7 100644
--- a/wrap/pybind11/tests/test_exceptions.cpp
+++ b/wrap/pybind11/tests/test_exceptions.cpp
@@ -105,11 +105,6 @@ struct PythonAlreadySetInDestructor {
     py::str s;
 };
 
-std::string error_already_set_what(const py::object &exc_type, const py::object &exc_value) {
-    PyErr_SetObject(exc_type.ptr(), exc_value.ptr());
-    return py::error_already_set().what();
-}
-
 TEST_SUBMODULE(exceptions, m) {
     m.def("throw_std_exception",
           []() { throw std::runtime_error("This exception was intentionally thrown."); });
@@ -334,4 +329,19 @@ TEST_SUBMODULE(exceptions, m) {
             e.restore();
         }
     });
+
+    // https://github.com/pybind/pybind11/issues/4075
+    m.def("test_pypy_oserror_normalization", []() {
+        try {
+            py::module_::import("io").attr("open")("this_filename_must_not_exist", "r");
+        } catch (const py::error_already_set &e) {
+            return py::str(e.what()); // str must be built before e goes out of scope.
+        }
+        return py::str("UNEXPECTED");
+    });
+
+    m.def("test_fn_cast_int", [](const py::function &fn) {
+        // function returns None instead of int, should give a useful error message
+        fn().cast<int>();
+    });
 }
diff --git a/wrap/pybind11/tests/test_exceptions.py b/wrap/pybind11/tests/test_exceptions.py
index a5984a142..ccac4536d 100644
--- a/wrap/pybind11/tests/test_exceptions.py
+++ b/wrap/pybind11/tests/test_exceptions.py
@@ -4,6 +4,7 @@ import pytest
 
 import env
 import pybind11_cross_module_tests as cm
+import pybind11_tests  # noqa: F401
 from pybind11_tests import exceptions as m
 
 
@@ -72,9 +73,9 @@ def test_cross_module_exceptions(msg):
 
 # TODO: FIXME
 @pytest.mark.xfail(
-    "env.PYPY and env.MACOS",
+    "env.MACOS and (env.PYPY or pybind11_tests.compiler_info.startswith('Homebrew Clang'))",
     raises=RuntimeError,
-    reason="Expected failure with PyPy and libc++ (Issue #2847 & PR #2999)",
+    reason="See Issue #2847, PR #2999, PR #4324",
 )
 def test_cross_module_exception_translator():
     with pytest.raises(KeyError):
@@ -93,8 +94,7 @@ def ignore_pytest_unraisable_warning(f):
     if hasattr(pytest, unraisable):  # Python >= 3.8 and pytest >= 6
         dec = pytest.mark.filterwarnings(f"ignore::pytest.{unraisable}")
         return dec(f)
-    else:
-        return f
+    return f
 
 
 # TODO: find out why this fails on PyPy, https://foss.heptapod.net/pypy/pypy/-/issues/3583
@@ -182,11 +182,11 @@ def test_custom(msg):
         m.throws5_1()
     assert msg(excinfo.value) == "MyException5 subclass"
 
-    with pytest.raises(m.MyException5) as excinfo:
+    with pytest.raises(m.MyException5) as excinfo:  # noqa: PT012
         try:
             m.throws5()
-        except m.MyException5_1:
-            raise RuntimeError("Exception error: caught child from parent")
+        except m.MyException5_1 as err:
+            raise RuntimeError("Exception error: caught child from parent") from err
     assert msg(excinfo.value) == "this is a helper-defined translated exception"
 
 
@@ -211,7 +211,7 @@ def test_nested_throws(capture):
         m.try_catch(m.MyException5, throw_myex)
     assert str(excinfo.value) == "nested error"
 
-    def pycatch(exctype, f, *args):
+    def pycatch(exctype, f, *args):  # noqa: ARG001
         try:
             f(*args)
         except m.MyException as e:
@@ -275,6 +275,20 @@ def test_local_translator(msg):
     assert msg(excinfo.value) == "this mod"
 
 
+def test_error_already_set_message_with_unicode_surrogate():  # Issue #4288
+    assert m.error_already_set_what(RuntimeError, "\ud927") == (
+        "RuntimeError: \\ud927",
+        False,
+    )
+
+
+def test_error_already_set_message_with_malformed_utf8():
+    assert m.error_already_set_what(RuntimeError, b"\x80") == (
+        "RuntimeError: b'\\x80'",
+        False,
+    )
+
+
 class FlakyException(Exception):
     def __init__(self, failure_point):
         if failure_point == "failure_point_init":
@@ -288,12 +302,12 @@ class FlakyException(Exception):
 
 
 @pytest.mark.parametrize(
-    "exc_type, exc_value, expected_what",
-    (
+    ("exc_type", "exc_value", "expected_what"),
+    [
         (ValueError, "plain_str", "ValueError: plain_str"),
         (ValueError, ("tuple_elem",), "ValueError: tuple_elem"),
         (FlakyException, ("happy",), "FlakyException: FlakyException.__str__"),
-    ),
+    ],
 )
 def test_error_already_set_what_with_happy_exceptions(
     exc_type, exc_value, expected_what
@@ -303,8 +317,7 @@ def test_error_already_set_what_with_happy_exceptions(
     assert what == expected_what
 
 
-@pytest.mark.skipif("env.PYPY", reason="PyErr_NormalizeException Segmentation fault")
-def test_flaky_exception_failure_point_init():
+def _test_flaky_exception_failure_point_init_before_py_3_12():
     with pytest.raises(RuntimeError) as excinfo:
         m.error_already_set_what(FlakyException, ("failure_point_init",))
     lines = str(excinfo.value).splitlines()
@@ -318,7 +331,33 @@ def test_flaky_exception_failure_point_init():
     # Checking the first two lines of the traceback as formatted in error_string():
     assert "test_exceptions.py(" in lines[3]
     assert lines[3].endswith("): __init__")
-    assert lines[4].endswith("): test_flaky_exception_failure_point_init")
+    assert lines[4].endswith(
+        "): _test_flaky_exception_failure_point_init_before_py_3_12"
+    )
+
+
+def _test_flaky_exception_failure_point_init_py_3_12():
+    # Behavior change in Python 3.12: https://github.com/python/cpython/issues/102594
+    what, py_err_set_after_what = m.error_already_set_what(
+        FlakyException, ("failure_point_init",)
+    )
+    assert not py_err_set_after_what
+    lines = what.splitlines()
+    assert lines[0].endswith("ValueError[WITH __notes__]: triggered_failure_point_init")
+    assert lines[1] == "__notes__ (len=1):"
+    assert "Normalization failed:" in lines[2]
+    assert "FlakyException" in lines[2]
+
+
+@pytest.mark.skipif(
+    "env.PYPY and sys.version_info[:2] < (3, 12)",
+    reason="PyErr_NormalizeException Segmentation fault",
+)
+def test_flaky_exception_failure_point_init():
+    if sys.version_info[:2] < (3, 12):
+        _test_flaky_exception_failure_point_init_before_py_3_12()
+    else:
+        _test_flaky_exception_failure_point_init_py_3_12()
 
 
 def test_flaky_exception_failure_point_str():
@@ -327,10 +366,7 @@ def test_flaky_exception_failure_point_str():
     )
     assert not py_err_set_after_what
     lines = what.splitlines()
-    if env.PYPY and len(lines) == 3:
-        n = 3  # Traceback is missing.
-    else:
-        n = 5
+    n = 3 if env.PYPY and len(lines) == 3 else 5
     assert (
         lines[:n]
         == [
@@ -360,3 +396,18 @@ def test_error_already_set_double_restore():
         "Internal error: pybind11::detail::error_fetch_and_normalize::restore()"
         " called a second time. ORIGINAL ERROR: ValueError: Random error."
     )
+
+
+def test_pypy_oserror_normalization():
+    # https://github.com/pybind/pybind11/issues/4075
+    what = m.test_pypy_oserror_normalization()
+    assert "this_filename_must_not_exist" in what
+
+
+def test_fn_cast_int_exception():
+    with pytest.raises(RuntimeError) as excinfo:
+        m.test_fn_cast_int(lambda: None)
+
+    assert str(excinfo.value).startswith(
+        "Unable to cast Python instance of type <class 'NoneType'> to C++ type"
+    )
diff --git a/wrap/pybind11/tests/test_factory_constructors.py b/wrap/pybind11/tests/test_factory_constructors.py
index 120a587c4..04df80260 100644
--- a/wrap/pybind11/tests/test_factory_constructors.py
+++ b/wrap/pybind11/tests/test_factory_constructors.py
@@ -96,7 +96,7 @@ def test_init_factory_signature(msg):
         3. __init__(self: m.factory_constructors.TestFactory1, arg0: m.factory_constructors.tag.pointer_tag) -> None
 
         4. __init__(self: m.factory_constructors.TestFactory1, arg0: handle, arg1: int, arg2: handle) -> None
-    """  # noqa: E501 line too long
+    """
     )
 
 
diff --git a/wrap/pybind11/tests/test_gil_scoped.cpp b/wrap/pybind11/tests/test_gil_scoped.cpp
index 97efdc161..f136086e8 100644
--- a/wrap/pybind11/tests/test_gil_scoped.cpp
+++ b/wrap/pybind11/tests/test_gil_scoped.cpp
@@ -11,6 +11,13 @@
 
 #include "pybind11_tests.h"
 
+#include <string>
+#include <thread>
+
+#define CROSS_MODULE(Function)                                                                    \
+    auto cm = py::module_::import("cross_module_gil_utils");                                      \
+    auto target = reinterpret_cast<void (*)()>(PyLong_AsVoidPtr(cm.attr(Function).ptr()));
+
 class VirtClass {
 public:
     virtual ~VirtClass() = default;
@@ -28,6 +35,16 @@ class PyVirtClass : public VirtClass {
 };
 
 TEST_SUBMODULE(gil_scoped, m) {
+    m.attr("defined_THREAD_SANITIZER") =
+#if defined(THREAD_SANITIZER)
+        true;
+#else
+        false;
+#endif
+
+    m.def("intentional_deadlock",
+          []() { std::thread([]() { py::gil_scoped_acquire gil_acquired; }).join(); });
+
     py::class_<VirtClass, PyVirtClass>(m, "VirtClass")
         .def(py::init<>())
         .def("virtual_func", &VirtClass::virtual_func)
@@ -37,11 +54,91 @@ TEST_SUBMODULE(gil_scoped, m) {
     m.def("test_callback_std_func", [](const std::function<void()> &func) { func(); });
     m.def("test_callback_virtual_func", [](VirtClass &virt) { virt.virtual_func(); });
     m.def("test_callback_pure_virtual_func", [](VirtClass &virt) { virt.pure_virtual_func(); });
-    m.def("test_cross_module_gil", []() {
-        auto cm = py::module_::import("cross_module_gil_utils");
-        auto gil_acquire = reinterpret_cast<void (*)()>(
-            PyLong_AsVoidPtr(cm.attr("gil_acquire_funcaddr").ptr()));
+    m.def("test_cross_module_gil_released", []() {
+        CROSS_MODULE("gil_acquire_funcaddr")
         py::gil_scoped_release gil_release;
-        gil_acquire();
+        target();
+    });
+    m.def("test_cross_module_gil_acquired", []() {
+        CROSS_MODULE("gil_acquire_funcaddr")
+        py::gil_scoped_acquire gil_acquire;
+        target();
+    });
+    m.def("test_cross_module_gil_inner_custom_released", []() {
+        CROSS_MODULE("gil_acquire_inner_custom_funcaddr")
+        py::gil_scoped_release gil_release;
+        target();
+    });
+    m.def("test_cross_module_gil_inner_custom_acquired", []() {
+        CROSS_MODULE("gil_acquire_inner_custom_funcaddr")
+        py::gil_scoped_acquire gil_acquire;
+        target();
+    });
+    m.def("test_cross_module_gil_inner_pybind11_released", []() {
+        CROSS_MODULE("gil_acquire_inner_pybind11_funcaddr")
+        py::gil_scoped_release gil_release;
+        target();
+    });
+    m.def("test_cross_module_gil_inner_pybind11_acquired", []() {
+        CROSS_MODULE("gil_acquire_inner_pybind11_funcaddr")
+        py::gil_scoped_acquire gil_acquire;
+        target();
+    });
+    m.def("test_cross_module_gil_nested_custom_released", []() {
+        CROSS_MODULE("gil_acquire_nested_custom_funcaddr")
+        py::gil_scoped_release gil_release;
+        target();
+    });
+    m.def("test_cross_module_gil_nested_custom_acquired", []() {
+        CROSS_MODULE("gil_acquire_nested_custom_funcaddr")
+        py::gil_scoped_acquire gil_acquire;
+        target();
+    });
+    m.def("test_cross_module_gil_nested_pybind11_released", []() {
+        CROSS_MODULE("gil_acquire_nested_pybind11_funcaddr")
+        py::gil_scoped_release gil_release;
+        target();
+    });
+    m.def("test_cross_module_gil_nested_pybind11_acquired", []() {
+        CROSS_MODULE("gil_acquire_nested_pybind11_funcaddr")
+        py::gil_scoped_acquire gil_acquire;
+        target();
+    });
+    m.def("test_release_acquire", [](const py::object &obj) {
+        py::gil_scoped_release gil_released;
+        py::gil_scoped_acquire gil_acquired;
+        return py::str(obj);
+    });
+    m.def("test_nested_acquire", [](const py::object &obj) {
+        py::gil_scoped_release gil_released;
+        py::gil_scoped_acquire gil_acquired_outer;
+        py::gil_scoped_acquire gil_acquired_inner;
+        return py::str(obj);
+    });
+    m.def("test_multi_acquire_release_cross_module", [](unsigned bits) {
+        py::set internals_ids;
+        internals_ids.add(PYBIND11_INTERNALS_ID);
+        {
+            py::gil_scoped_release gil_released;
+            auto thread_f = [bits, &internals_ids]() {
+                py::gil_scoped_acquire gil_acquired;
+                auto cm = py::module_::import("cross_module_gil_utils");
+                auto target = reinterpret_cast<std::string (*)(unsigned)>(
+                    PyLong_AsVoidPtr(cm.attr("gil_multi_acquire_release_funcaddr").ptr()));
+                std::string cm_internals_id = target(bits >> 3);
+                internals_ids.add(cm_internals_id);
+            };
+            if ((bits & 0x1u) != 0u) {
+                thread_f();
+            }
+            if ((bits & 0x2u) != 0u) {
+                std::thread non_python_thread(thread_f);
+                non_python_thread.join();
+            }
+            if ((bits & 0x4u) != 0u) {
+                thread_f();
+            }
+        }
+        return internals_ids;
     });
 }
diff --git a/wrap/pybind11/tests/test_gil_scoped.py b/wrap/pybind11/tests/test_gil_scoped.py
index 52374b0cc..fc8af9b77 100644
--- a/wrap/pybind11/tests/test_gil_scoped.py
+++ b/wrap/pybind11/tests/test_gil_scoped.py
@@ -1,45 +1,197 @@
 import multiprocessing
+import sys
 import threading
+import time
 
+import pytest
+
+import env
 from pybind11_tests import gil_scoped as m
 
 
+class ExtendedVirtClass(m.VirtClass):
+    def virtual_func(self):
+        pass
+
+    def pure_virtual_func(self):
+        pass
+
+
+def test_callback_py_obj():
+    m.test_callback_py_obj(lambda: None)
+
+
+def test_callback_std_func():
+    m.test_callback_std_func(lambda: None)
+
+
+def test_callback_virtual_func():
+    extended = ExtendedVirtClass()
+    m.test_callback_virtual_func(extended)
+
+
+def test_callback_pure_virtual_func():
+    extended = ExtendedVirtClass()
+    m.test_callback_pure_virtual_func(extended)
+
+
+def test_cross_module_gil_released():
+    """Makes sure that the GIL can be acquired by another module from a GIL-released state."""
+    m.test_cross_module_gil_released()  # Should not raise a SIGSEGV
+
+
+def test_cross_module_gil_acquired():
+    """Makes sure that the GIL can be acquired by another module from a GIL-acquired state."""
+    m.test_cross_module_gil_acquired()  # Should not raise a SIGSEGV
+
+
+def test_cross_module_gil_inner_custom_released():
+    """Makes sure that the GIL can be acquired/released by another module
+    from a GIL-released state using custom locking logic."""
+    m.test_cross_module_gil_inner_custom_released()
+
+
+def test_cross_module_gil_inner_custom_acquired():
+    """Makes sure that the GIL can be acquired/acquired by another module
+    from a GIL-acquired state using custom locking logic."""
+    m.test_cross_module_gil_inner_custom_acquired()
+
+
+def test_cross_module_gil_inner_pybind11_released():
+    """Makes sure that the GIL can be acquired/released by another module
+    from a GIL-released state using pybind11 locking logic."""
+    m.test_cross_module_gil_inner_pybind11_released()
+
+
+def test_cross_module_gil_inner_pybind11_acquired():
+    """Makes sure that the GIL can be acquired/acquired by another module
+    from a GIL-acquired state using pybind11 locking logic."""
+    m.test_cross_module_gil_inner_pybind11_acquired()
+
+
+def test_cross_module_gil_nested_custom_released():
+    """Makes sure that the GIL can be nested acquired/released by another module
+    from a GIL-released state using custom locking logic."""
+    m.test_cross_module_gil_nested_custom_released()
+
+
+def test_cross_module_gil_nested_custom_acquired():
+    """Makes sure that the GIL can be nested acquired/acquired by another module
+    from a GIL-acquired state using custom locking logic."""
+    m.test_cross_module_gil_nested_custom_acquired()
+
+
+def test_cross_module_gil_nested_pybind11_released():
+    """Makes sure that the GIL can be nested acquired/released by another module
+    from a GIL-released state using pybind11 locking logic."""
+    m.test_cross_module_gil_nested_pybind11_released()
+
+
+def test_cross_module_gil_nested_pybind11_acquired():
+    """Makes sure that the GIL can be nested acquired/acquired by another module
+    from a GIL-acquired state using pybind11 locking logic."""
+    m.test_cross_module_gil_nested_pybind11_acquired()
+
+
+def test_release_acquire():
+    assert m.test_release_acquire(0xAB) == "171"
+
+
+def test_nested_acquire():
+    assert m.test_nested_acquire(0xAB) == "171"
+
+
+def test_multi_acquire_release_cross_module():
+    for bits in range(16 * 8):
+        internals_ids = m.test_multi_acquire_release_cross_module(bits)
+        assert len(internals_ids) == 2 if bits % 8 else 1
+
+
+# Intentionally putting human review in the loop here, to guard against accidents.
+VARS_BEFORE_ALL_BASIC_TESTS = dict(vars())  # Make a copy of the dict (critical).
+ALL_BASIC_TESTS = (
+    test_callback_py_obj,
+    test_callback_std_func,
+    test_callback_virtual_func,
+    test_callback_pure_virtual_func,
+    test_cross_module_gil_released,
+    test_cross_module_gil_acquired,
+    test_cross_module_gil_inner_custom_released,
+    test_cross_module_gil_inner_custom_acquired,
+    test_cross_module_gil_inner_pybind11_released,
+    test_cross_module_gil_inner_pybind11_acquired,
+    test_cross_module_gil_nested_custom_released,
+    test_cross_module_gil_nested_custom_acquired,
+    test_cross_module_gil_nested_pybind11_released,
+    test_cross_module_gil_nested_pybind11_acquired,
+    test_release_acquire,
+    test_nested_acquire,
+    test_multi_acquire_release_cross_module,
+)
+
+
+def test_all_basic_tests_completeness():
+    num_found = 0
+    for key, value in VARS_BEFORE_ALL_BASIC_TESTS.items():
+        if not key.startswith("test_"):
+            continue
+        assert value in ALL_BASIC_TESTS
+        num_found += 1
+    assert len(ALL_BASIC_TESTS) == num_found
+
+
+def _intentional_deadlock():
+    m.intentional_deadlock()
+
+
+ALL_BASIC_TESTS_PLUS_INTENTIONAL_DEADLOCK = ALL_BASIC_TESTS + (_intentional_deadlock,)
+
+
 def _run_in_process(target, *args, **kwargs):
-    """Runs target in process and returns its exitcode after 10s (None if still alive)."""
+    test_fn = target if len(args) == 0 else args[0]
+    # Do not need to wait much, 10s should be more than enough.
+    timeout = 0.1 if test_fn is _intentional_deadlock else 10
     process = multiprocessing.Process(target=target, args=args, kwargs=kwargs)
     process.daemon = True
     try:
+        t_start = time.time()
         process.start()
-        # Do not need to wait much, 10s should be more than enough.
-        process.join(timeout=10)
+        if timeout >= 100:  # For debugging.
+            print(
+                "\nprocess.pid STARTED", process.pid, (sys.argv, target, args, kwargs)
+            )
+            print(f"COPY-PASTE-THIS: gdb {sys.argv[0]} -p {process.pid}", flush=True)
+        process.join(timeout=timeout)
+        if timeout >= 100:
+            print("\nprocess.pid JOINED", process.pid, flush=True)
+        t_delta = time.time() - t_start
+        if process.exitcode == 66 and m.defined_THREAD_SANITIZER:  # Issue #2754
+            # WOULD-BE-NICE-TO-HAVE: Check that the message below is actually in the output.
+            # Maybe this could work:
+            # https://gist.github.com/alexeygrigorev/01ce847f2e721b513b42ea4a6c96905e
+            pytest.skip(
+                "ThreadSanitizer: starting new threads after multi-threaded fork is not supported."
+            )
+        elif test_fn is _intentional_deadlock:
+            assert process.exitcode is None
+            return 0
+
+        if process.exitcode is None:
+            assert t_delta > 0.9 * timeout
+            msg = "DEADLOCK, most likely, exactly what this test is meant to detect."
+            if env.PYPY and env.WIN:
+                pytest.skip(msg)
+            raise RuntimeError(msg)
         return process.exitcode
     finally:
         if process.is_alive():
             process.terminate()
 
 
-def _python_to_cpp_to_python():
-    """Calls different C++ functions that come back to Python."""
-
-    class ExtendedVirtClass(m.VirtClass):
-        def virtual_func(self):
-            pass
-
-        def pure_virtual_func(self):
-            pass
-
-    extended = ExtendedVirtClass()
-    m.test_callback_py_obj(lambda: None)
-    m.test_callback_std_func(lambda: None)
-    m.test_callback_virtual_func(extended)
-    m.test_callback_pure_virtual_func(extended)
-
-
-def _python_to_cpp_to_python_from_threads(num_threads, parallel=False):
-    """Calls different C++ functions that come back to Python, from Python threads."""
+def _run_in_threads(test_fn, num_threads, parallel):
     threads = []
     for _ in range(num_threads):
-        thread = threading.Thread(target=_python_to_cpp_to_python)
+        thread = threading.Thread(target=test_fn)
         thread.daemon = True
         thread.start()
         if parallel:
@@ -51,43 +203,40 @@ def _python_to_cpp_to_python_from_threads(num_threads, parallel=False):
 
 
 # TODO: FIXME, sometimes returns -11 (segfault) instead of 0 on macOS Python 3.9
-def test_python_to_cpp_to_python_from_thread():
+@pytest.mark.parametrize("test_fn", ALL_BASIC_TESTS_PLUS_INTENTIONAL_DEADLOCK)
+def test_run_in_process_one_thread(test_fn):
     """Makes sure there is no GIL deadlock when running in a thread.
 
     It runs in a separate process to be able to stop and assert if it deadlocks.
     """
-    assert _run_in_process(_python_to_cpp_to_python_from_threads, 1) == 0
+    assert _run_in_process(_run_in_threads, test_fn, num_threads=1, parallel=False) == 0
 
 
 # TODO: FIXME on macOS Python 3.9
-def test_python_to_cpp_to_python_from_thread_multiple_parallel():
+@pytest.mark.parametrize("test_fn", ALL_BASIC_TESTS_PLUS_INTENTIONAL_DEADLOCK)
+def test_run_in_process_multiple_threads_parallel(test_fn):
     """Makes sure there is no GIL deadlock when running in a thread multiple times in parallel.
 
     It runs in a separate process to be able to stop and assert if it deadlocks.
     """
-    assert _run_in_process(_python_to_cpp_to_python_from_threads, 8, parallel=True) == 0
+    assert _run_in_process(_run_in_threads, test_fn, num_threads=8, parallel=True) == 0
 
 
 # TODO: FIXME on macOS Python 3.9
-def test_python_to_cpp_to_python_from_thread_multiple_sequential():
+@pytest.mark.parametrize("test_fn", ALL_BASIC_TESTS_PLUS_INTENTIONAL_DEADLOCK)
+def test_run_in_process_multiple_threads_sequential(test_fn):
     """Makes sure there is no GIL deadlock when running in a thread multiple times sequentially.
 
     It runs in a separate process to be able to stop and assert if it deadlocks.
     """
-    assert (
-        _run_in_process(_python_to_cpp_to_python_from_threads, 8, parallel=False) == 0
-    )
+    assert _run_in_process(_run_in_threads, test_fn, num_threads=8, parallel=False) == 0
 
 
 # TODO: FIXME on macOS Python 3.9
-def test_python_to_cpp_to_python_from_process():
+@pytest.mark.parametrize("test_fn", ALL_BASIC_TESTS_PLUS_INTENTIONAL_DEADLOCK)
+def test_run_in_process_direct(test_fn):
     """Makes sure there is no GIL deadlock when using processes.
 
     This test is for completion, but it was never an issue.
     """
-    assert _run_in_process(_python_to_cpp_to_python) == 0
-
-
-def test_cross_module_gil():
-    """Makes sure that the GIL can be acquired by another module from a GIL-released state."""
-    m.test_cross_module_gil()  # Should not raise a SIGSEGV
+    assert _run_in_process(test_fn) == 0
diff --git a/wrap/pybind11/tests/test_iostream.py b/wrap/pybind11/tests/test_iostream.py
index 5bbdf6955..d283eb152 100644
--- a/wrap/pybind11/tests/test_iostream.py
+++ b/wrap/pybind11/tests/test_iostream.py
@@ -9,16 +9,16 @@ def test_captured(capsys):
     m.captured_output(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
 
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
 
     m.captured_err(msg)
     stdout, stderr = capsys.readouterr()
-    assert stdout == ""
+    assert not stdout
     assert stderr == msg
 
 
@@ -30,7 +30,7 @@ def test_captured_large_string(capsys):
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
 
 
 def test_captured_utf8_2byte_offset0(capsys):
@@ -40,7 +40,7 @@ def test_captured_utf8_2byte_offset0(capsys):
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
 
 
 def test_captured_utf8_2byte_offset1(capsys):
@@ -50,7 +50,7 @@ def test_captured_utf8_2byte_offset1(capsys):
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
 
 
 def test_captured_utf8_3byte_offset0(capsys):
@@ -60,7 +60,7 @@ def test_captured_utf8_3byte_offset0(capsys):
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
 
 
 def test_captured_utf8_3byte_offset1(capsys):
@@ -70,7 +70,7 @@ def test_captured_utf8_3byte_offset1(capsys):
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
 
 
 def test_captured_utf8_3byte_offset2(capsys):
@@ -80,7 +80,7 @@ def test_captured_utf8_3byte_offset2(capsys):
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
 
 
 def test_captured_utf8_4byte_offset0(capsys):
@@ -90,7 +90,7 @@ def test_captured_utf8_4byte_offset0(capsys):
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
 
 
 def test_captured_utf8_4byte_offset1(capsys):
@@ -100,7 +100,7 @@ def test_captured_utf8_4byte_offset1(capsys):
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
 
 
 def test_captured_utf8_4byte_offset2(capsys):
@@ -110,7 +110,7 @@ def test_captured_utf8_4byte_offset2(capsys):
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
 
 
 def test_captured_utf8_4byte_offset3(capsys):
@@ -120,7 +120,7 @@ def test_captured_utf8_4byte_offset3(capsys):
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
 
 
 def test_guard_capture(capsys):
@@ -128,7 +128,7 @@ def test_guard_capture(capsys):
     m.guard_output(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
 
 
 def test_series_captured(capture):
@@ -145,7 +145,7 @@ def test_flush(capfd):
     with m.ostream_redirect():
         m.noisy_function(msg, flush=False)
         stdout, stderr = capfd.readouterr()
-        assert stdout == ""
+        assert not stdout
 
         m.noisy_function(msg2, flush=True)
         stdout, stderr = capfd.readouterr()
@@ -164,15 +164,15 @@ def test_not_captured(capfd):
         m.raw_output(msg)
     stdout, stderr = capfd.readouterr()
     assert stdout == msg
-    assert stderr == ""
-    assert stream.getvalue() == ""
+    assert not stderr
+    assert not stream.getvalue()
 
     stream = StringIO()
     with redirect_stdout(stream):
         m.captured_output(msg)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ""
-    assert stderr == ""
+    assert not stdout
+    assert not stderr
     assert stream.getvalue() == msg
 
 
@@ -182,16 +182,16 @@ def test_err(capfd):
     with redirect_stderr(stream):
         m.raw_err(msg)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ""
+    assert not stdout
     assert stderr == msg
-    assert stream.getvalue() == ""
+    assert not stream.getvalue()
 
     stream = StringIO()
     with redirect_stderr(stream):
         m.captured_err(msg)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ""
-    assert stderr == ""
+    assert not stdout
+    assert not stderr
     assert stream.getvalue() == msg
 
 
@@ -221,14 +221,13 @@ def test_redirect(capfd):
         m.raw_output(msg)
     stdout, stderr = capfd.readouterr()
     assert stdout == msg
-    assert stream.getvalue() == ""
+    assert not stream.getvalue()
 
     stream = StringIO()
-    with redirect_stdout(stream):
-        with m.ostream_redirect():
-            m.raw_output(msg)
+    with redirect_stdout(stream), m.ostream_redirect():
+        m.raw_output(msg)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ""
+    assert not stdout
     assert stream.getvalue() == msg
 
     stream = StringIO()
@@ -236,7 +235,7 @@ def test_redirect(capfd):
         m.raw_output(msg)
     stdout, stderr = capfd.readouterr()
     assert stdout == msg
-    assert stream.getvalue() == ""
+    assert not stream.getvalue()
 
 
 def test_redirect_err(capfd):
@@ -244,13 +243,12 @@ def test_redirect_err(capfd):
     msg2 = "StdErr"
 
     stream = StringIO()
-    with redirect_stderr(stream):
-        with m.ostream_redirect(stdout=False):
-            m.raw_output(msg)
-            m.raw_err(msg2)
+    with redirect_stderr(stream), m.ostream_redirect(stdout=False):
+        m.raw_output(msg)
+        m.raw_err(msg2)
     stdout, stderr = capfd.readouterr()
     assert stdout == msg
-    assert stderr == ""
+    assert not stderr
     assert stream.getvalue() == msg2
 
 
@@ -260,14 +258,12 @@ def test_redirect_both(capfd):
 
     stream = StringIO()
     stream2 = StringIO()
-    with redirect_stdout(stream):
-        with redirect_stderr(stream2):
-            with m.ostream_redirect():
-                m.raw_output(msg)
-                m.raw_err(msg2)
+    with redirect_stdout(stream), redirect_stderr(stream2), m.ostream_redirect():
+        m.raw_output(msg)
+        m.raw_err(msg2)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ""
-    assert stderr == ""
+    assert not stdout
+    assert not stderr
     assert stream.getvalue() == msg
     assert stream2.getvalue() == msg2
 
diff --git a/wrap/pybind11/tests/test_kwargs_and_defaults.cpp b/wrap/pybind11/tests/test_kwargs_and_defaults.cpp
index 7418afefb..77e72c0c7 100644
--- a/wrap/pybind11/tests/test_kwargs_and_defaults.cpp
+++ b/wrap/pybind11/tests/test_kwargs_and_defaults.cpp
@@ -43,7 +43,15 @@ TEST_SUBMODULE(kwargs_and_defaults, m) {
     m.def("kw_func_udl_z", kw_func, "x"_a, "y"_a = 0);
 
     // test_args_and_kwargs
-    m.def("args_function", [](py::args args) -> py::tuple { return std::move(args); });
+    m.def("args_function", [](py::args args) -> py::tuple {
+        PYBIND11_WARNING_PUSH
+
+#ifdef PYBIND11_DETECTED_CLANG_WITH_MISLEADING_CALL_STD_MOVE_EXPLICITLY_WARNING
+        PYBIND11_WARNING_DISABLE_CLANG("-Wreturn-std-move")
+#endif
+        return args;
+        PYBIND11_WARNING_POP
+    });
     m.def("args_kwargs_function", [](const py::args &args, const py::kwargs &kwargs) {
         return py::make_tuple(args, kwargs);
     });
diff --git a/wrap/pybind11/tests/test_kwargs_and_defaults.py b/wrap/pybind11/tests/test_kwargs_and_defaults.py
index ab7017886..7174726fc 100644
--- a/wrap/pybind11/tests/test_kwargs_and_defaults.py
+++ b/wrap/pybind11/tests/test_kwargs_and_defaults.py
@@ -25,7 +25,7 @@ def test_function_signatures(doc):
     )
 
 
-def test_named_arguments(msg):
+def test_named_arguments():
     assert m.kw_func0(5, 10) == "x=5, y=10"
 
     assert m.kw_func1(5, 10) == "x=5, y=10"
@@ -43,8 +43,7 @@ def test_named_arguments(msg):
         # noinspection PyArgumentList
         m.kw_func2(x=5, y=10, z=12)
     assert excinfo.match(
-        r"(?s)^kw_func2\(\): incompatible.*Invoked with: kwargs: ((x=5|y=10|z=12)(, |$))"
-        + "{3}$"
+        r"(?s)^kw_func2\(\): incompatible.*Invoked with: kwargs: ((x=5|y=10|z=12)(, |$)){3}$"
     )
 
     assert m.kw_func4() == "{13 17}"
@@ -59,7 +58,7 @@ def test_arg_and_kwargs():
     assert m.args_function(*args) == args
 
     args = "a1", "a2"
-    kwargs = dict(arg3="a3", arg4=4)
+    kwargs = {"arg3": "a3", "arg4": 4}
     assert m.args_kwargs_function(*args, **kwargs) == (args, kwargs)
 
 
@@ -177,7 +176,7 @@ def test_mixed_args_and_kwargs(msg):
 
     assert (
         m.args_kwonly_kwargs_defaults.__doc__
-        == "args_kwonly_kwargs_defaults(i: int = 1, j: float = 3.14159, *args, z: int = 42, **kwargs) -> tuple\n"  # noqa: E501 line too long
+        == "args_kwonly_kwargs_defaults(i: int = 1, j: float = 3.14159, *args, z: int = 42, **kwargs) -> tuple\n"
     )
     assert m.args_kwonly_kwargs_defaults() == (1, 3.14159, (), 42, {})
     assert m.args_kwonly_kwargs_defaults(2) == (2, 3.14159, (), 42, {})
@@ -233,15 +232,15 @@ def test_keyword_only_args(msg):
     x.method(i=1, j=2)
     assert (
         m.first_arg_kw_only.__init__.__doc__
-        == "__init__(self: pybind11_tests.kwargs_and_defaults.first_arg_kw_only, *, i: int = 0) -> None\n"  # noqa: E501 line too long
+        == "__init__(self: pybind11_tests.kwargs_and_defaults.first_arg_kw_only, *, i: int = 0) -> None\n"
     )
     assert (
         m.first_arg_kw_only.method.__doc__
-        == "method(self: pybind11_tests.kwargs_and_defaults.first_arg_kw_only, *, i: int = 1, j: int = 2) -> None\n"  # noqa: E501 line too long
+        == "method(self: pybind11_tests.kwargs_and_defaults.first_arg_kw_only, *, i: int = 1, j: int = 2) -> None\n"
     )
 
 
-def test_positional_only_args(msg):
+def test_positional_only_args():
     assert m.pos_only_all(1, 2) == (1, 2)
     assert m.pos_only_all(2, 1) == (2, 1)
 
@@ -283,7 +282,7 @@ def test_positional_only_args(msg):
     # Mix it with args and kwargs:
     assert (
         m.args_kwonly_full_monty.__doc__
-        == "args_kwonly_full_monty(arg0: int = 1, arg1: int = 2, /, j: float = 3.14159, *args, z: int = 42, **kwargs) -> tuple\n"  # noqa: E501 line too long
+        == "args_kwonly_full_monty(arg0: int = 1, arg1: int = 2, /, j: float = 3.14159, *args, z: int = 42, **kwargs) -> tuple\n"
     )
     assert m.args_kwonly_full_monty() == (1, 2, 3.14159, (), 42, {})
     assert m.args_kwonly_full_monty(8) == (8, 2, 3.14159, (), 42, {})
@@ -326,18 +325,18 @@ def test_positional_only_args(msg):
     # https://github.com/pybind/pybind11/pull/3402#issuecomment-963341987
     assert (
         m.first_arg_kw_only.pos_only.__doc__
-        == "pos_only(self: pybind11_tests.kwargs_and_defaults.first_arg_kw_only, /, i: int, j: int) -> None\n"  # noqa: E501 line too long
+        == "pos_only(self: pybind11_tests.kwargs_and_defaults.first_arg_kw_only, /, i: int, j: int) -> None\n"
     )
 
 
 def test_signatures():
-    assert "kw_only_all(*, i: int, j: int) -> tuple\n" == m.kw_only_all.__doc__
-    assert "kw_only_mixed(i: int, *, j: int) -> tuple\n" == m.kw_only_mixed.__doc__
-    assert "pos_only_all(i: int, j: int, /) -> tuple\n" == m.pos_only_all.__doc__
-    assert "pos_only_mix(i: int, /, j: int) -> tuple\n" == m.pos_only_mix.__doc__
+    assert m.kw_only_all.__doc__ == "kw_only_all(*, i: int, j: int) -> tuple\n"
+    assert m.kw_only_mixed.__doc__ == "kw_only_mixed(i: int, *, j: int) -> tuple\n"
+    assert m.pos_only_all.__doc__ == "pos_only_all(i: int, j: int, /) -> tuple\n"
+    assert m.pos_only_mix.__doc__ == "pos_only_mix(i: int, /, j: int) -> tuple\n"
     assert (
-        "pos_kw_only_mix(i: int, /, j: int, *, k: int) -> tuple\n"
-        == m.pos_kw_only_mix.__doc__
+        m.pos_kw_only_mix.__doc__
+        == "pos_kw_only_mix(i: int, /, j: int, *, k: int) -> tuple\n"
     )
 
 
diff --git a/wrap/pybind11/tests/test_local_bindings.py b/wrap/pybind11/tests/test_local_bindings.py
index 654d96d49..d64187739 100644
--- a/wrap/pybind11/tests/test_local_bindings.py
+++ b/wrap/pybind11/tests/test_local_bindings.py
@@ -130,7 +130,8 @@ def test_stl_bind_global():
 def test_mixed_local_global():
     """Local types take precedence over globally registered types: a module with a `module_local`
     type can be registered even if the type is already registered globally.  With the module,
-    casting will go to the local type; outside the module casting goes to the global type."""
+    casting will go to the local type; outside the module casting goes to the global type.
+    """
     import pybind11_cross_module_tests as cm
 
     m.register_mixed_global()
diff --git a/wrap/pybind11/tests/test_methods_and_attributes.cpp b/wrap/pybind11/tests/test_methods_and_attributes.cpp
index 815dd5e98..31d46eb7e 100644
--- a/wrap/pybind11/tests/test_methods_and_attributes.cpp
+++ b/wrap/pybind11/tests/test_methods_and_attributes.cpp
@@ -177,6 +177,38 @@ struct RValueRefParam {
     std::size_t func4(std::string &&s) const & { return s.size(); }
 };
 
+namespace pybind11_tests {
+namespace exercise_is_setter {
+
+struct FieldBase {
+    int int_value() const { return int_value_; }
+
+    FieldBase &SetIntValue(int int_value) {
+        int_value_ = int_value;
+        return *this;
+    }
+
+private:
+    int int_value_ = -99;
+};
+
+struct Field : FieldBase {};
+
+void add_bindings(py::module &m) {
+    py::module sm = m.def_submodule("exercise_is_setter");
+    // NOTE: FieldBase is not wrapped, therefore ...
+    py::class_<Field>(sm, "Field")
+        .def(py::init<>())
+        .def_property(
+            "int_value",
+            &Field::int_value,
+            &Field::SetIntValue // ... the `FieldBase &` return value here cannot be converted.
+        );
+}
+
+} // namespace exercise_is_setter
+} // namespace pybind11_tests
+
 TEST_SUBMODULE(methods_and_attributes, m) {
     // test_methods_and_attributes
     py::class_<ExampleMandA> emna(m, "ExampleMandA");
@@ -456,4 +488,6 @@ TEST_SUBMODULE(methods_and_attributes, m) {
         .def("func2", &RValueRefParam::func2)
         .def("func3", &RValueRefParam::func3)
         .def("func4", &RValueRefParam::func4);
+
+    pybind11_tests::exercise_is_setter::add_bindings(m);
 }
diff --git a/wrap/pybind11/tests/test_methods_and_attributes.py b/wrap/pybind11/tests/test_methods_and_attributes.py
index 0a2ae1239..955a85f67 100644
--- a/wrap/pybind11/tests/test_methods_and_attributes.py
+++ b/wrap/pybind11/tests/test_methods_and_attributes.py
@@ -183,9 +183,9 @@ def test_static_properties():
 
     # Only static attributes can be deleted
     del m.TestPropertiesOverride.def_readonly_static
+    assert hasattr(m.TestPropertiesOverride, "def_readonly_static")
     assert (
-        hasattr(m.TestPropertiesOverride, "def_readonly_static")
-        and m.TestPropertiesOverride.def_readonly_static
+        m.TestPropertiesOverride.def_readonly_static
         is m.TestProperties.def_readonly_static
     )
     assert "def_readonly_static" not in m.TestPropertiesOverride.__dict__
@@ -256,10 +256,7 @@ def test_no_mixed_overloads():
 
 @pytest.mark.parametrize("access", ["ro", "rw", "static_ro", "static_rw"])
 def test_property_return_value_policies(access):
-    if not access.startswith("static"):
-        obj = m.TestPropRVP()
-    else:
-        obj = m.TestPropRVP
+    obj = m.TestPropRVP() if not access.startswith("static") else m.TestPropRVP
 
     ref = getattr(obj, access + "_ref")
     assert ref.value == 1
@@ -525,3 +522,12 @@ def test_rvalue_ref_param():
     assert r.func2("1234") == 4
     assert r.func3("12345") == 5
     assert r.func4("123456") == 6
+
+
+def test_is_setter():
+    fld = m.exercise_is_setter.Field()
+    assert fld.int_value == -99
+    setter_return = fld.int_value = 100
+    assert isinstance(setter_return, int)
+    assert setter_return == 100
+    assert fld.int_value == 100
diff --git a/wrap/pybind11/tests/test_modules.py b/wrap/pybind11/tests/test_modules.py
index e11d68e78..2f6d825b7 100644
--- a/wrap/pybind11/tests/test_modules.py
+++ b/wrap/pybind11/tests/test_modules.py
@@ -1,3 +1,5 @@
+import builtins
+
 import pytest
 
 import env
@@ -61,7 +63,6 @@ def test_importing():
     from pybind11_tests.modules import OD
 
     assert OD is OrderedDict
-    assert str(OD([(1, "a"), (2, "b")])) == "OrderedDict([(1, 'a'), (2, 'b')])"
 
 
 def test_pydoc():
@@ -86,12 +87,7 @@ def test_builtin_key_type():
 
     Previous versions of pybind11 would add a unicode key in python 2.
     """
-    if hasattr(__builtins__, "keys"):
-        keys = __builtins__.keys()
-    else:  # this is to make pypy happy since builtins is different there.
-        keys = __builtins__.__dict__.keys()
-
-    assert {type(k) for k in keys} == {str}
+    assert all(type(k) == str for k in dir(builtins))
 
 
 @pytest.mark.xfail("env.PYPY", reason="PyModule_GetName()")
@@ -107,11 +103,10 @@ def test_def_submodule_failures():
         sm_name_orig = sm.__name__
         sm.__name__ = malformed_utf8
         try:
-            with pytest.raises(Exception):
-                # Seen with Python 3.9: SystemError: nameless module
-                # But we do not want to exercise the internals of PyModule_GetName(), which could
-                # change in future versions of Python, but a bad __name__ is very likely to cause
-                # some kind of failure indefinitely.
+            # We want to assert that a bad __name__ causes some kind of failure, although we do not want to exercise
+            # the internals of PyModule_GetName(). Currently all supported Python versions raise SystemError. If that
+            # changes in future Python versions, simply add the new expected exception types here.
+            with pytest.raises(SystemError):
                 m.def_submodule(sm, b"SubSubModuleName")
         finally:
             # Clean up to ensure nothing gets upset by a module with an invalid __name__.
diff --git a/wrap/pybind11/tests/test_numpy_array.cpp b/wrap/pybind11/tests/test_numpy_array.cpp
index 69ddbe1ef..8c122a865 100644
--- a/wrap/pybind11/tests/test_numpy_array.cpp
+++ b/wrap/pybind11/tests/test_numpy_array.cpp
@@ -521,4 +521,32 @@ TEST_SUBMODULE(numpy_array, sm) {
     sm.def("test_fmt_desc_double", [](const py::array_t<double> &) {});
     sm.def("test_fmt_desc_const_float", [](const py::array_t<const float> &) {});
     sm.def("test_fmt_desc_const_double", [](const py::array_t<const double> &) {});
+
+    sm.def("round_trip_float", [](double d) { return d; });
+
+    sm.def("pass_array_pyobject_ptr_return_sum_str_values",
+           [](const py::array_t<PyObject *> &objs) {
+               std::string sum_str_values;
+               for (const auto &obj : objs) {
+                   sum_str_values += py::str(obj.attr("value"));
+               }
+               return sum_str_values;
+           });
+
+    sm.def("pass_array_pyobject_ptr_return_as_list",
+           [](const py::array_t<PyObject *> &objs) -> py::list { return objs; });
+
+    sm.def("return_array_pyobject_ptr_cpp_loop", [](const py::list &objs) {
+        py::size_t arr_size = py::len(objs);
+        py::array_t<PyObject *> arr_from_list(static_cast<py::ssize_t>(arr_size));
+        PyObject **data = arr_from_list.mutable_data();
+        for (py::size_t i = 0; i < arr_size; i++) {
+            assert(data[i] == nullptr);
+            data[i] = py::cast<PyObject *>(objs[i].attr("value"));
+        }
+        return arr_from_list;
+    });
+
+    sm.def("return_array_pyobject_ptr_from_list",
+           [](const py::list &objs) -> py::array_t<PyObject *> { return objs; });
 }
diff --git a/wrap/pybind11/tests/test_numpy_array.py b/wrap/pybind11/tests/test_numpy_array.py
index 504963b16..12e7d17d1 100644
--- a/wrap/pybind11/tests/test_numpy_array.py
+++ b/wrap/pybind11/tests/test_numpy_array.py
@@ -22,7 +22,7 @@ def test_dtypes():
             )
 
 
-@pytest.fixture(scope="function")
+@pytest.fixture()
 def arr():
     return np.array([[1, 2, 3], [4, 5, 6]], "=u2")
 
@@ -67,7 +67,7 @@ def test_array_attributes():
 
 
 @pytest.mark.parametrize(
-    "args, ret", [([], 0), ([0], 0), ([1], 3), ([0, 1], 1), ([1, 2], 5)]
+    ("args", "ret"), [([], 0), ([0], 0), ([1], 3), ([0, 1], 1), ([1, 2], 5)]
 )
 def test_index_offset(arr, args, ret):
     assert m.index_at(arr, *args) == ret
@@ -93,7 +93,7 @@ def test_dim_check_fail(arr):
 
 
 @pytest.mark.parametrize(
-    "args, ret",
+    ("args", "ret"),
     [
         ([], [1, 2, 3, 4, 5, 6]),
         ([1], [4, 5, 6]),
@@ -211,12 +211,14 @@ def test_wrap():
             assert b[0, 0] == 1234
 
     a1 = np.array([1, 2], dtype=np.int16)
-    assert a1.flags.owndata and a1.base is None
+    assert a1.flags.owndata
+    assert a1.base is None
     a2 = m.wrap(a1)
     assert_references(a1, a2)
 
     a1 = np.array([[1, 2], [3, 4]], dtype=np.float32, order="F")
-    assert a1.flags.owndata and a1.base is None
+    assert a1.flags.owndata
+    assert a1.base is None
     a2 = m.wrap(a1)
     assert_references(a1, a2)
 
@@ -451,13 +453,15 @@ def test_array_resize():
     try:
         m.array_resize3(a, 3, True)
     except ValueError as e:
-        assert str(e).startswith("cannot resize an array")
+        assert str(e).startswith("cannot resize an array")  # noqa: PT017
     # transposed array doesn't own data
     b = a.transpose()
     try:
         m.array_resize3(b, 3, False)
     except ValueError as e:
-        assert str(e).startswith("cannot resize this array: it does not own its data")
+        assert str(e).startswith(  # noqa: PT017
+            "cannot resize this array: it does not own its data"
+        )
     # ... but reshape should be fine
     m.array_reshape2(b)
     assert b.shape == (8, 8)
@@ -585,3 +589,80 @@ def test_dtype_refcount_leak():
     m.ndim(a)
     after = getrefcount(dtype)
     assert after == before
+
+
+def test_round_trip_float():
+    arr = np.zeros((), np.float64)
+    arr[()] = 37.2
+    assert m.round_trip_float(arr) == 37.2
+
+
+# HINT: An easy and robust way (although only manual unfortunately) to check for
+#       ref-count leaks in the test_.*pyobject_ptr.* functions below is to
+#           * temporarily insert `while True:` (one-by-one),
+#           * run this test, and
+#           * run the Linux `top` command in another shell to visually monitor
+#             `RES` for a minute or two.
+#       If there is a leak, it is usually evident in seconds because the `RES`
+#       value increases without bounds. (Don't forget to Ctrl-C the test!)
+
+
+# For use as a temporary user-defined object, to maximize sensitivity of the tests below:
+#     * Ref-count leaks will be immediately evident.
+#     * Sanitizers are much more likely to detect heap-use-after-free due to
+#       other ref-count bugs.
+class PyValueHolder:
+    def __init__(self, value):
+        self.value = value
+
+
+def WrapWithPyValueHolder(*values):
+    return [PyValueHolder(v) for v in values]
+
+
+def UnwrapPyValueHolder(vhs):
+    return [vh.value for vh in vhs]
+
+
+def test_pass_array_pyobject_ptr_return_sum_str_values_ndarray():
+    # Intentionally all temporaries, do not change.
+    assert (
+        m.pass_array_pyobject_ptr_return_sum_str_values(
+            np.array(WrapWithPyValueHolder(-3, "four", 5.0), dtype=object)
+        )
+        == "-3four5.0"
+    )
+
+
+def test_pass_array_pyobject_ptr_return_sum_str_values_list():
+    # Intentionally all temporaries, do not change.
+    assert (
+        m.pass_array_pyobject_ptr_return_sum_str_values(
+            WrapWithPyValueHolder(2, "three", -4.0)
+        )
+        == "2three-4.0"
+    )
+
+
+def test_pass_array_pyobject_ptr_return_as_list():
+    # Intentionally all temporaries, do not change.
+    assert UnwrapPyValueHolder(
+        m.pass_array_pyobject_ptr_return_as_list(
+            np.array(WrapWithPyValueHolder(-1, "two", 3.0), dtype=object)
+        )
+    ) == [-1, "two", 3.0]
+
+
+@pytest.mark.parametrize(
+    ("return_array_pyobject_ptr", "unwrap"),
+    [
+        (m.return_array_pyobject_ptr_cpp_loop, list),
+        (m.return_array_pyobject_ptr_from_list, UnwrapPyValueHolder),
+    ],
+)
+def test_return_array_pyobject_ptr_cpp_loop(return_array_pyobject_ptr, unwrap):
+    # Intentionally all temporaries, do not change.
+    arr_from_list = return_array_pyobject_ptr(WrapWithPyValueHolder(6, "seven", -8.0))
+    assert isinstance(arr_from_list, np.ndarray)
+    assert arr_from_list.dtype == np.dtype("O")
+    assert unwrap(arr_from_list) == [6, "seven", -8.0]
diff --git a/wrap/pybind11/tests/test_numpy_dtypes.py b/wrap/pybind11/tests/test_numpy_dtypes.py
index fcfd587b1..d10457eeb 100644
--- a/wrap/pybind11/tests/test_numpy_dtypes.py
+++ b/wrap/pybind11/tests/test_numpy_dtypes.py
@@ -130,14 +130,10 @@ def test_dtype(simple_dtype):
         partial_nested_fmt(),
         "[('a','S3'),('b','S3')]",
         (
-            "{{'names':['a','b','c','d'],"
-            + "'formats':[('S4',(3,)),('"
-            + e
-            + "i4',(2,)),('u1',(3,)),('"
-            + e
-            + "f4',(4,2))],"
-            + "'offsets':[0,12,20,24],'itemsize':56}}"
-        ).format(e=e),
+            "{'names':['a','b','c','d'],"
+            f"'formats':[('S4',(3,)),('{e}i4',(2,)),('u1',(3,)),('{e}f4',(4,2))],"
+            "'offsets':[0,12,20,24],'itemsize':56}"
+        ),
         "[('e1','" + e + "i8'),('e2','u1')]",
         "[('x','i1'),('y','" + e + "u8')]",
         "[('cflt','" + e + "c8'),('cdbl','" + e + "c16')]",
@@ -291,19 +287,17 @@ def test_array_array():
 
     arr = m.create_array_array(3)
     assert str(arr.dtype).replace(" ", "") == (
-        "{{'names':['a','b','c','d'],"
-        + "'formats':[('S4',(3,)),('"
-        + e
-        + "i4',(2,)),('u1',(3,)),('{e}f4',(4,2))],"
-        + "'offsets':[0,12,20,24],'itemsize':56}}"
-    ).format(e=e)
+        "{'names':['a','b','c','d'],"
+        f"'formats':[('S4',(3,)),('{e}i4',(2,)),('u1',(3,)),('{e}f4',(4,2))],"
+        "'offsets':[0,12,20,24],'itemsize':56}"
+    )
     assert m.print_array_array(arr) == [
         "a={{A,B,C,D},{K,L,M,N},{U,V,W,X}},b={0,1},"
-        + "c={0,1,2},d={{0,1},{10,11},{20,21},{30,31}}",
+        "c={0,1,2},d={{0,1},{10,11},{20,21},{30,31}}",
         "a={{W,X,Y,Z},{G,H,I,J},{Q,R,S,T}},b={1000,1001},"
-        + "c={10,11,12},d={{100,101},{110,111},{120,121},{130,131}}",
+        "c={10,11,12},d={{100,101},{110,111},{120,121},{130,131}}",
         "a={{S,T,U,V},{C,D,E,F},{M,N,O,P}},b={2000,2001},"
-        + "c={20,21,22},d={{200,201},{210,211},{220,221},{230,231}}",
+        "c={20,21,22},d={{200,201},{210,211},{220,221},{230,231}}",
     ]
     assert arr["a"].tolist() == [
         [b"ABCD", b"KLMN", b"UVWX"],
diff --git a/wrap/pybind11/tests/test_numpy_vectorize.py b/wrap/pybind11/tests/test_numpy_vectorize.py
index 7e8c015c4..f1e8b6254 100644
--- a/wrap/pybind11/tests/test_numpy_vectorize.py
+++ b/wrap/pybind11/tests/test_numpy_vectorize.py
@@ -149,7 +149,7 @@ def test_docs(doc):
         doc(m.vectorized_func)
         == """
         vectorized_func(arg0: numpy.ndarray[numpy.int32], arg1: numpy.ndarray[numpy.float32], arg2: numpy.ndarray[numpy.float64]) -> object
-    """  # noqa: E501 line too long
+    """
     )
 
 
diff --git a/wrap/pybind11/tests/test_operator_overloading.cpp b/wrap/pybind11/tests/test_operator_overloading.cpp
index a4b895a89..112a363b4 100644
--- a/wrap/pybind11/tests/test_operator_overloading.cpp
+++ b/wrap/pybind11/tests/test_operator_overloading.cpp
@@ -132,22 +132,18 @@ struct hash<HashMe> {
 // Not a good abs function, but easy to test.
 std::string abs(const Vector2 &) { return "abs(Vector2)"; }
 
-// MSVC & Intel warns about unknown pragmas, and warnings are errors.
-#if !defined(_MSC_VER) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic push
 // clang 7.0.0 and Apple LLVM 10.0.1 introduce `-Wself-assign-overloaded` to
 // `-Wall`, which is used here for overloading (e.g. `py::self += py::self `).
-// Here, we suppress the warning using `#pragma diagnostic`.
+// Here, we suppress the warning
 // Taken from: https://github.com/RobotLocomotion/drake/commit/aaf84b46
 // TODO(eric): This could be resolved using a function / functor (e.g. `py::self()`).
-#    if defined(__APPLE__) && defined(__clang__)
-#        if (__clang_major__ >= 10)
-#            pragma GCC diagnostic ignored "-Wself-assign-overloaded"
-#        endif
-#    elif defined(__clang__)
-#        if (__clang_major__ >= 7)
-#            pragma GCC diagnostic ignored "-Wself-assign-overloaded"
-#        endif
+#if defined(__APPLE__) && defined(__clang__)
+#    if (__clang_major__ >= 10)
+PYBIND11_WARNING_DISABLE_CLANG("-Wself-assign-overloaded")
+#    endif
+#elif defined(__clang__)
+#    if (__clang_major__ >= 7)
+PYBIND11_WARNING_DISABLE_CLANG("-Wself-assign-overloaded")
 #    endif
 #endif
 
@@ -283,6 +279,3 @@ TEST_SUBMODULE(operators, m) {
 
     m.def("get_unhashable_HashMe_set", []() { return std::unordered_set<HashMe>{{"one"}}; });
 }
-#if !defined(_MSC_VER) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic pop
-#endif
diff --git a/wrap/pybind11/tests/test_operator_overloading.py b/wrap/pybind11/tests/test_operator_overloading.py
index b228da3cc..9fde305a0 100644
--- a/wrap/pybind11/tests/test_operator_overloading.py
+++ b/wrap/pybind11/tests/test_operator_overloading.py
@@ -130,7 +130,6 @@ def test_nested():
 
 
 def test_overriding_eq_reset_hash():
-
     assert m.Comparable(15) is not m.Comparable(15)
     assert m.Comparable(15) == m.Comparable(15)
 
diff --git a/wrap/pybind11/tests/test_pytypes.cpp b/wrap/pybind11/tests/test_pytypes.cpp
index f532e2608..b4ee64289 100644
--- a/wrap/pybind11/tests/test_pytypes.cpp
+++ b/wrap/pybind11/tests/test_pytypes.cpp
@@ -99,6 +99,8 @@ void m_defs(py::module_ &m) {
 } // namespace handle_from_move_only_type_with_operator_PyObject
 
 TEST_SUBMODULE(pytypes, m) {
+    m.def("obj_class_name", [](py::handle obj) { return py::detail::obj_class_name(obj.ptr()); });
+
     handle_from_move_only_type_with_operator_PyObject::m_defs(m);
 
     // test_bool
@@ -109,6 +111,11 @@ TEST_SUBMODULE(pytypes, m) {
     m.def("get_iterator", [] { return py::iterator(); });
     // test_iterable
     m.def("get_iterable", [] { return py::iterable(); });
+    m.def("get_frozenset_from_iterable",
+          [](const py::iterable &iter) { return py::frozenset(iter); });
+    m.def("get_list_from_iterable", [](const py::iterable &iter) { return py::list(iter); });
+    m.def("get_set_from_iterable", [](const py::iterable &iter) { return py::set(iter); });
+    m.def("get_tuple_from_iterable", [](const py::iterable &iter) { return py::tuple(iter); });
     // test_float
     m.def("get_float", [] { return py::float_(0.0f); });
     // test_list
@@ -178,7 +185,7 @@ TEST_SUBMODULE(pytypes, m) {
         return d2;
     });
     m.def("dict_contains",
-          [](const py::dict &dict, py::object val) { return dict.contains(val); });
+          [](const py::dict &dict, const py::object &val) { return dict.contains(val); });
     m.def("dict_contains",
           [](const py::dict &dict, const char *val) { return dict.contains(val); });
 
@@ -201,7 +208,12 @@ TEST_SUBMODULE(pytypes, m) {
     m.def("str_from_char_ssize_t", []() { return py::str{"red", (py::ssize_t) 3}; });
     m.def("str_from_char_size_t", []() { return py::str{"blue", (py::size_t) 4}; });
     m.def("str_from_string", []() { return py::str(std::string("baz")); });
+    m.def("str_from_std_string_input", [](const std::string &stri) { return py::str(stri); });
+    m.def("str_from_cstr_input", [](const char *c_str) { return py::str(c_str); });
     m.def("str_from_bytes", []() { return py::str(py::bytes("boo", 3)); });
+    m.def("str_from_bytes_input",
+          [](const py::bytes &encoded_str) { return py::str(encoded_str); });
+
     m.def("str_from_object", [](const py::object &obj) { return py::str(obj); });
     m.def("repr_from_object", [](const py::object &obj) { return py::repr(obj); });
     m.def("str_from_handle", [](py::handle h) { return py::str(h); });
@@ -248,6 +260,15 @@ TEST_SUBMODULE(pytypes, m) {
         });
     });
 
+    m.def("return_capsule_with_destructor_3", []() {
+        py::print("creating capsule");
+        auto cap = py::capsule((void *) 1233, "oname", [](void *ptr) {
+            py::print("destructing capsule: {}"_s.format((size_t) ptr));
+        });
+        py::print("original name: {}"_s.format(cap.name()));
+        return cap;
+    });
+
     m.def("return_renamed_capsule_with_destructor_2", []() {
         py::print("creating capsule");
         auto cap = py::capsule((void *) 1234, [](void *ptr) {
@@ -284,6 +305,12 @@ TEST_SUBMODULE(pytypes, m) {
         return capsule;
     });
 
+    m.def("return_capsule_with_explicit_nullptr_dtor", []() {
+        py::print("creating capsule with explicit nullptr dtor");
+        return py::capsule(reinterpret_cast<void *>(1234),
+                           static_cast<void (*)(void *)>(nullptr)); // PR #4221
+    });
+
     // test_accessors
     m.def("accessor_api", [](const py::object &o) {
         auto d = py::dict();
@@ -527,6 +554,9 @@ TEST_SUBMODULE(pytypes, m) {
 
     m.def("hash_function", [](py::object obj) { return py::hash(std::move(obj)); });
 
+    m.def("obj_contains",
+          [](py::object &obj, const py::object &key) { return obj.contains(key); });
+
     m.def("test_number_protocol", [](const py::object &a, const py::object &b) {
         py::list l;
         l.append(a.equal(b));
@@ -756,4 +786,38 @@ TEST_SUBMODULE(pytypes, m) {
         }
         return o;
     });
+
+    // testing immutable object augmented assignment: #issue 3812
+    m.def("inplace_append", [](py::object &a, const py::object &b) {
+        a += b;
+        return a;
+    });
+    m.def("inplace_subtract", [](py::object &a, const py::object &b) {
+        a -= b;
+        return a;
+    });
+    m.def("inplace_multiply", [](py::object &a, const py::object &b) {
+        a *= b;
+        return a;
+    });
+    m.def("inplace_divide", [](py::object &a, const py::object &b) {
+        a /= b;
+        return a;
+    });
+    m.def("inplace_or", [](py::object &a, const py::object &b) {
+        a |= b;
+        return a;
+    });
+    m.def("inplace_and", [](py::object &a, const py::object &b) {
+        a &= b;
+        return a;
+    });
+    m.def("inplace_lshift", [](py::object &a, const py::object &b) {
+        a <<= b;
+        return a;
+    });
+    m.def("inplace_rshift", [](py::object &a, const py::object &b) {
+        a >>= b;
+        return a;
+    });
 }
diff --git a/wrap/pybind11/tests/test_pytypes.py b/wrap/pybind11/tests/test_pytypes.py
index 7a0a8b4ab..eda7a20a9 100644
--- a/wrap/pybind11/tests/test_pytypes.py
+++ b/wrap/pybind11/tests/test_pytypes.py
@@ -9,7 +9,13 @@ from pybind11_tests import detailed_error_messages_enabled
 from pybind11_tests import pytypes as m
 
 
-def test_handle_from_move_only_type_with_operator_PyObject():  # noqa: N802
+def test_obj_class_name():
+    assert m.obj_class_name(None) == "NoneType"
+    assert m.obj_class_name(list) == "list"
+    assert m.obj_class_name([]) == "list"
+
+
+def test_handle_from_move_only_type_with_operator_PyObject():
     assert m.handle_from_move_only_type_with_operator_PyObject_ncnst()
     assert m.handle_from_move_only_type_with_operator_PyObject_const()
 
@@ -26,6 +32,22 @@ def test_iterator(doc):
     assert doc(m.get_iterator) == "get_iterator() -> Iterator"
 
 
+@pytest.mark.parametrize(
+    ("pytype", "from_iter_func"),
+    [
+        (frozenset, m.get_frozenset_from_iterable),
+        (list, m.get_list_from_iterable),
+        (set, m.get_set_from_iterable),
+        (tuple, m.get_tuple_from_iterable),
+    ],
+)
+def test_from_iterable(pytype, from_iter_func):
+    my_iter = iter(range(10))
+    s = from_iter_func(my_iter)
+    assert type(s) == pytype
+    assert s == pytype(range(10))
+
+
 def test_iterable(doc):
     assert doc(m.get_iterable) == "get_iterable() -> Iterable"
 
@@ -65,7 +87,7 @@ def test_list(capture, doc):
     assert doc(m.print_list) == "print_list(arg0: list) -> None"
 
 
-def test_none(capture, doc):
+def test_none(doc):
     assert doc(m.get_none) == "get_none() -> None"
     assert doc(m.print_none) == "print_none(arg0: None) -> None"
 
@@ -152,6 +174,31 @@ def test_dict(capture, doc):
     assert m.dict_keyword_constructor() == {"x": 1, "y": 2, "z": 3}
 
 
+class CustomContains:
+    d = {"key": None}
+
+    def __contains__(self, m):
+        return m in self.d
+
+
+@pytest.mark.parametrize(
+    ("arg", "func"),
+    [
+        (set(), m.anyset_contains),
+        ({}, m.dict_contains),
+        (CustomContains(), m.obj_contains),
+    ],
+)
+@pytest.mark.xfail("env.PYPY and sys.pypy_version_info < (7, 3, 10)", strict=False)
+def test_unhashable_exceptions(arg, func):
+    class Unhashable:
+        __hash__ = None
+
+    with pytest.raises(TypeError) as exc_info:
+        func(arg, Unhashable())
+    assert "unhashable type:" in str(exc_info.value)
+
+
 def test_tuple():
     assert m.tuple_no_args() == ()
     assert m.tuple_ssize_t() == ()
@@ -203,6 +250,20 @@ def test_str(doc):
         m.str_from_string_from_str(ucs_surrogates_str)
 
 
+@pytest.mark.parametrize(
+    "func",
+    [
+        m.str_from_bytes_input,
+        m.str_from_cstr_input,
+        m.str_from_std_string_input,
+    ],
+)
+def test_surrogate_pairs_unicode_error(func):
+    input_str = "\ud83d\ude4f".encode("utf-8", "surrogatepass")
+    with pytest.raises(UnicodeDecodeError):
+        func(input_str)
+
+
 def test_bytes(doc):
     assert m.bytes_from_char_ssize_t().decode() == "green"
     assert m.bytes_from_char_size_t().decode() == "purple"
@@ -212,7 +273,7 @@ def test_bytes(doc):
     assert doc(m.bytes_from_str) == "bytes_from_str() -> bytes"
 
 
-def test_bytearray(doc):
+def test_bytearray():
     assert m.bytearray_from_char_ssize_t().decode() == "$%"
     assert m.bytearray_from_char_size_t().decode() == "@$!"
     assert m.bytearray_from_string().decode() == "foo"
@@ -258,6 +319,19 @@ def test_capsule(capture):
     """
     )
 
+    with capture:
+        a = m.return_capsule_with_destructor_3()
+        del a
+        pytest.gc_collect()
+    assert (
+        capture.unordered
+        == """
+        creating capsule
+        destructing capsule: 1233
+        original name: oname
+    """
+    )
+
     with capture:
         a = m.return_renamed_capsule_with_destructor_2()
         del a
@@ -283,6 +357,17 @@ def test_capsule(capture):
     """
     )
 
+    with capture:
+        a = m.return_capsule_with_explicit_nullptr_dtor()
+        del a
+        pytest.gc_collect()
+    assert (
+        capture.unordered
+        == """
+        creating capsule with explicit nullptr dtor
+    """
+    )
+
 
 def test_accessors():
     class SubTestObject:
@@ -313,7 +398,7 @@ def test_accessors():
     assert d["implicit_list"] == [1, 2, 3]
     assert all(x in TestObject.__dict__ for x in d["implicit_dict"])
 
-    assert m.tuple_accessor(tuple()) == (0, 1, 2)
+    assert m.tuple_accessor(()) == (0, 1, 2)
 
     d = m.accessor_assignment()
     assert d["get"] == 0
@@ -403,7 +488,7 @@ def test_pybind11_str_raw_str():
     assert cvt({}) == "{}"
     assert cvt({3: 4}) == "{3: 4}"
     assert cvt(set()) == "set()"
-    assert cvt({3, 3}) == "{3}"
+    assert cvt({3}) == "{3}"
 
     valid_orig = "DZ"
     valid_utf8 = valid_orig.encode("utf-8")
@@ -464,7 +549,7 @@ def test_print(capture):
     assert str(excinfo.value) == "Unable to convert call argument " + (
         "'1' of type 'UnregisteredType' to Python object"
         if detailed_error_messages_enabled
-        else "to Python object (#define PYBIND11_DETAILED_ERROR_MESSAGES or compile in debug mode for details)"
+        else "'1' to Python object (#define PYBIND11_DETAILED_ERROR_MESSAGES or compile in debug mode for details)"
     )
 
 
@@ -521,7 +606,7 @@ def test_issue2361():
 
 
 @pytest.mark.parametrize(
-    "method, args, fmt, expected_view",
+    ("method", "args", "fmt", "expected_view"),
     [
         (m.test_memoryview_object, (b"red",), "B", b"red"),
         (m.test_memoryview_buffer_info, (b"green",), "B", b"green"),
@@ -579,7 +664,7 @@ def test_memoryview_from_memory():
 
 
 def test_builtin_functions():
-    assert m.get_len([i for i in range(42)]) == 42
+    assert m.get_len(list(range(42))) == 42
     with pytest.raises(TypeError) as exc_info:
         m.get_len(i for i in range(42))
     assert str(exc_info.value) in [
@@ -623,7 +708,7 @@ def test_pass_bytes_or_unicode_to_string_types():
 
 
 @pytest.mark.parametrize(
-    "create_weakref, create_weakref_with_callback",
+    ("create_weakref", "create_weakref_with_callback"),
     [
         (m.weakref_from_handle, m.weakref_from_handle_and_function),
         (m.weakref_from_object, m.weakref_from_object_and_function),
@@ -638,7 +723,7 @@ def test_weakref(create_weakref, create_weakref_with_callback):
 
     callback_called = False
 
-    def callback(wr):
+    def callback(_):
         nonlocal callback_called
         callback_called = True
 
@@ -658,7 +743,7 @@ def test_weakref(create_weakref, create_weakref_with_callback):
 
 
 @pytest.mark.parametrize(
-    "create_weakref, has_callback",
+    ("create_weakref", "has_callback"),
     [
         (m.weakref_from_handle, False),
         (m.weakref_from_object, False),
@@ -676,10 +761,7 @@ def test_weakref_err(create_weakref, has_callback):
     ob = C()
     # Should raise TypeError on CPython
     with pytest.raises(TypeError) if not env.PYPY else contextlib.nullcontext():
-        if has_callback:
-            _ = create_weakref(ob, callback)
-        else:
-            _ = create_weakref(ob)
+        _ = create_weakref(ob, callback) if has_callback else create_weakref(ob)
 
 
 def test_cpp_iterators():
@@ -739,3 +821,78 @@ def test_populate_obj_str_attrs():
     new_attrs = {k: v for k, v in new_o.__dict__.items() if not k.startswith("_")}
     assert all(isinstance(v, str) for v in new_attrs.values())
     assert len(new_attrs) == pop
+
+
+@pytest.mark.parametrize(
+    ("a", "b"),
+    [("foo", "bar"), (1, 2), (1.0, 2.0), (list(range(3)), list(range(3, 6)))],
+)
+def test_inplace_append(a, b):
+    expected = a + b
+    assert m.inplace_append(a, b) == expected
+
+
+@pytest.mark.parametrize(
+    ("a", "b"), [(3, 2), (3.0, 2.0), (set(range(3)), set(range(2)))]
+)
+def test_inplace_subtract(a, b):
+    expected = a - b
+    assert m.inplace_subtract(a, b) == expected
+
+
+@pytest.mark.parametrize(("a", "b"), [(3, 2), (3.0, 2.0), ([1], 3)])
+def test_inplace_multiply(a, b):
+    expected = a * b
+    assert m.inplace_multiply(a, b) == expected
+
+
+@pytest.mark.parametrize(("a", "b"), [(6, 3), (6.0, 3.0)])
+def test_inplace_divide(a, b):
+    expected = a / b
+    assert m.inplace_divide(a, b) == expected
+
+
+@pytest.mark.parametrize(
+    ("a", "b"),
+    [
+        (False, True),
+        (
+            set(),
+            {
+                1,
+            },
+        ),
+    ],
+)
+def test_inplace_or(a, b):
+    expected = a | b
+    assert m.inplace_or(a, b) == expected
+
+
+@pytest.mark.parametrize(
+    ("a", "b"),
+    [
+        (True, False),
+        (
+            {1, 2, 3},
+            {
+                1,
+            },
+        ),
+    ],
+)
+def test_inplace_and(a, b):
+    expected = a & b
+    assert m.inplace_and(a, b) == expected
+
+
+@pytest.mark.parametrize(("a", "b"), [(8, 1), (-3, 2)])
+def test_inplace_lshift(a, b):
+    expected = a << b
+    assert m.inplace_lshift(a, b) == expected
+
+
+@pytest.mark.parametrize(("a", "b"), [(8, 1), (-2, 2)])
+def test_inplace_rshift(a, b):
+    expected = a >> b
+    assert m.inplace_rshift(a, b) == expected
diff --git a/wrap/pybind11/tests/test_sequences_and_iterators.cpp b/wrap/pybind11/tests/test_sequences_and_iterators.cpp
index b867f49a2..1de65edbf 100644
--- a/wrap/pybind11/tests/test_sequences_and_iterators.cpp
+++ b/wrap/pybind11/tests/test_sequences_and_iterators.cpp
@@ -559,4 +559,23 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
           []() { return py::make_iterator<py::return_value_policy::copy>(list); });
     m.def("make_iterator_2",
           []() { return py::make_iterator<py::return_value_policy::automatic>(list); });
+
+    // test_iterator on c arrays
+    // #4100: ensure lvalue required as increment operand
+    class CArrayHolder {
+    public:
+        CArrayHolder(double x, double y, double z) {
+            values[0] = x;
+            values[1] = y;
+            values[2] = z;
+        };
+        double values[3];
+    };
+
+    py::class_<CArrayHolder>(m, "CArrayHolder")
+        .def(py::init<double, double, double>())
+        .def(
+            "__iter__",
+            [](const CArrayHolder &v) { return py::make_iterator(v.values, v.values + 3); },
+            py::keep_alive<0, 1>());
 }
diff --git a/wrap/pybind11/tests/test_sequences_and_iterators.py b/wrap/pybind11/tests/test_sequences_and_iterators.py
index 062e3b3d3..dc129f2bf 100644
--- a/wrap/pybind11/tests/test_sequences_and_iterators.py
+++ b/wrap/pybind11/tests/test_sequences_and_iterators.py
@@ -1,5 +1,5 @@
 import pytest
-from pytest import approx
+from pytest import approx  # noqa: PT013
 
 from pybind11_tests import ConstructorStats
 from pybind11_tests import sequences_and_iterators as m
@@ -103,7 +103,8 @@ def test_sequence():
 
     assert "Sequence" in repr(s)
     assert len(s) == 5
-    assert s[0] == 0 and s[3] == 0
+    assert s[0] == 0
+    assert s[3] == 0
     assert 12.34 not in s
     s[0], s[3] = 12.34, 56.78
     assert 12.34 in s
@@ -241,3 +242,11 @@ def test_iterator_rvp():
     assert list(m.make_iterator_1()) == [1, 2, 3]
     assert list(m.make_iterator_2()) == [1, 2, 3]
     assert not isinstance(m.make_iterator_1(), type(m.make_iterator_2()))
+
+
+def test_carray_iterator():
+    """#4100: Check for proper iterator overload with C-Arrays"""
+    args_gt = [float(i) for i in range(3)]
+    arr_h = m.CArrayHolder(*args_gt)
+    args = list(arr_h)
+    assert args_gt == args
diff --git a/wrap/pybind11/tests/test_smart_ptr.cpp b/wrap/pybind11/tests/test_smart_ptr.cpp
index 2c23a9a19..6d9efcedc 100644
--- a/wrap/pybind11/tests/test_smart_ptr.cpp
+++ b/wrap/pybind11/tests/test_smart_ptr.cpp
@@ -266,14 +266,14 @@ struct ElementList {
 // It is always possible to construct a ref<T> from an Object* pointer without
 // possible inconsistencies, hence the 'true' argument at the end.
 // Make pybind11 aware of the non-standard getter member function
-namespace pybind11 {
+namespace PYBIND11_NAMESPACE {
 namespace detail {
 template <typename T>
 struct holder_helper<ref<T>> {
     static const T *get(const ref<T> &p) { return p.get_ptr(); }
 };
 } // namespace detail
-} // namespace pybind11
+} // namespace PYBIND11_NAMESPACE
 
 // Make pybind aware of the ref-counted wrapper type (s):
 PYBIND11_DECLARE_HOLDER_TYPE(T, ref<T>, true);
diff --git a/wrap/pybind11/tests/test_stl.cpp b/wrap/pybind11/tests/test_stl.cpp
index 38d32fda9..d45465d68 100644
--- a/wrap/pybind11/tests/test_stl.cpp
+++ b/wrap/pybind11/tests/test_stl.cpp
@@ -23,7 +23,7 @@
 #if defined(PYBIND11_TEST_BOOST)
 #    include <boost/optional.hpp>
 
-namespace pybind11 {
+namespace PYBIND11_NAMESPACE {
 namespace detail {
 template <typename T>
 struct type_caster<boost::optional<T>> : optional_caster<boost::optional<T>> {};
@@ -31,7 +31,7 @@ struct type_caster<boost::optional<T>> : optional_caster<boost::optional<T>> {};
 template <>
 struct type_caster<boost::none_t> : void_caster<boost::none_t> {};
 } // namespace detail
-} // namespace pybind11
+} // namespace PYBIND11_NAMESPACE
 #endif
 
 // Test with `std::variant` in C++17 mode, or with `boost::variant` in C++11/14
@@ -43,7 +43,7 @@ using std::variant;
 #    define PYBIND11_TEST_VARIANT 1
 using boost::variant;
 
-namespace pybind11 {
+namespace PYBIND11_NAMESPACE {
 namespace detail {
 template <typename... Ts>
 struct type_caster<boost::variant<Ts...>> : variant_caster<boost::variant<Ts...>> {};
@@ -56,7 +56,7 @@ struct visit_helper<boost::variant> {
     }
 };
 } // namespace detail
-} // namespace pybind11
+} // namespace PYBIND11_NAMESPACE
 #endif
 
 PYBIND11_MAKE_OPAQUE(std::vector<std::string, std::allocator<std::string>>);
@@ -159,13 +159,13 @@ private:
     std::vector<T> storage;
 };
 
-namespace pybind11 {
+namespace PYBIND11_NAMESPACE {
 namespace detail {
 template <typename T>
 struct type_caster<ReferenceSensitiveOptional<T>>
     : optional_caster<ReferenceSensitiveOptional<T>> {};
 } // namespace detail
-} // namespace pybind11
+} // namespace PYBIND11_NAMESPACE
 
 TEST_SUBMODULE(stl, m) {
     // test_vector
@@ -176,9 +176,14 @@ TEST_SUBMODULE(stl, m) {
     m.def("load_bool_vector",
           [](const std::vector<bool> &v) { return v.at(0) == true && v.at(1) == false; });
     // Unnumbered regression (caused by #936): pointers to stl containers aren't castable
-    static std::vector<RValueCaster> lvv{2};
     m.def(
-        "cast_ptr_vector", []() { return &lvv; }, py::return_value_policy::reference);
+        "cast_ptr_vector",
+        []() {
+            // Using no-destructor idiom to side-step warnings from overzealous compilers.
+            static auto *v = new std::vector<RValueCaster>{2};
+            return v;
+        },
+        py::return_value_policy::reference);
 
     // test_deque
     m.def("cast_deque", []() { return std::deque<int>{1}; });
@@ -237,6 +242,7 @@ TEST_SUBMODULE(stl, m) {
     lvn["b"].emplace_back();        // add a list
     lvn["b"].back().emplace_back(); // add an array
     lvn["b"].back().emplace_back(); // add another array
+    static std::vector<RValueCaster> lvv{2};
     m.def("cast_lv_vector", []() -> const decltype(lvv) & { return lvv; });
     m.def("cast_lv_array", []() -> const decltype(lva) & { return lva; });
     m.def("cast_lv_map", []() -> const decltype(lvm) & { return lvm; });
diff --git a/wrap/pybind11/tests/test_stl.py b/wrap/pybind11/tests/test_stl.py
index d30c38211..8a614f8b8 100644
--- a/wrap/pybind11/tests/test_stl.py
+++ b/wrap/pybind11/tests/test_stl.py
@@ -14,7 +14,7 @@ def test_vector(doc):
 
     assert m.cast_bool_vector() == [True, False]
     assert m.load_bool_vector([True, False])
-    assert m.load_bool_vector(tuple([True, False]))
+    assert m.load_bool_vector((True, False))
 
     assert doc(m.cast_vector) == "cast_vector() -> List[int]"
     assert doc(m.load_vector) == "load_vector(arg0: List[int]) -> bool"
@@ -23,7 +23,7 @@ def test_vector(doc):
     assert m.cast_ptr_vector() == ["lvalue", "lvalue"]
 
 
-def test_deque(doc):
+def test_deque():
     """std::deque <-> list"""
     lst = m.cast_deque()
     assert lst == [1]
@@ -39,8 +39,11 @@ def test_array(doc):
     assert m.load_array(lst)
     assert m.load_array(tuple(lst))
 
-    assert doc(m.cast_array) == "cast_array() -> List[int[2]]"
-    assert doc(m.load_array) == "load_array(arg0: List[int[2]]) -> bool"
+    assert doc(m.cast_array) == "cast_array() -> Annotated[List[int], FixedSize(2)]"
+    assert (
+        doc(m.load_array)
+        == "load_array(arg0: Annotated[List[int], FixedSize(2)]) -> bool"
+    )
 
 
 def test_valarray(doc):
@@ -95,7 +98,8 @@ def test_recursive_casting():
 
     # Issue #853 test case:
     z = m.cast_unique_ptr_vector()
-    assert z[0].value == 7 and z[1].value == 42
+    assert z[0].value == 7
+    assert z[1].value == 42
 
 
 def test_move_out_container():
@@ -366,7 +370,7 @@ def test_issue_1561():
     """check fix for issue #1561"""
     bar = m.Issue1561Outer()
     bar.list = [m.Issue1561Inner("bar")]
-    bar.list
+    assert bar.list
     assert bar.list[0].data == "bar"
 
 
diff --git a/wrap/pybind11/tests/test_stl_binders.cpp b/wrap/pybind11/tests/test_stl_binders.cpp
index ca9630bd1..1681760aa 100644
--- a/wrap/pybind11/tests/test_stl_binders.cpp
+++ b/wrap/pybind11/tests/test_stl_binders.cpp
@@ -70,6 +70,44 @@ NestMap *times_hundred(int n) {
     return m;
 }
 
+/*
+ * Recursive data structures as test for issue #4623
+ */
+struct RecursiveVector : std::vector<RecursiveVector> {
+    using Parent = std::vector<RecursiveVector>;
+    using Parent::Parent;
+};
+
+struct RecursiveMap : std::map<int, RecursiveMap> {
+    using Parent = std::map<int, RecursiveMap>;
+    using Parent::Parent;
+};
+
+/*
+ * Pybind11 does not catch more complicated recursion schemes, such as mutual
+ * recursion.
+ * In that case custom recursive_container_traits specializations need to be added,
+ * thus manually telling pybind11 about the recursion.
+ */
+struct MutuallyRecursiveContainerPairMV;
+struct MutuallyRecursiveContainerPairVM;
+
+struct MutuallyRecursiveContainerPairMV : std::map<int, MutuallyRecursiveContainerPairVM> {};
+struct MutuallyRecursiveContainerPairVM : std::vector<MutuallyRecursiveContainerPairMV> {};
+
+namespace pybind11 {
+namespace detail {
+template <typename SFINAE>
+struct recursive_container_traits<MutuallyRecursiveContainerPairMV, SFINAE> {
+    using type_to_check_recursively = recursive_bottom;
+};
+template <typename SFINAE>
+struct recursive_container_traits<MutuallyRecursiveContainerPairVM, SFINAE> {
+    using type_to_check_recursively = recursive_bottom;
+};
+} // namespace detail
+} // namespace pybind11
+
 TEST_SUBMODULE(stl_binders, m) {
     // test_vector_int
     py::bind_vector<std::vector<unsigned int>>(m, "VectorInt", py::buffer_protocol());
@@ -129,6 +167,12 @@ TEST_SUBMODULE(stl_binders, m) {
             m, "VectorUndeclStruct", py::buffer_protocol());
     });
 
+    // Bind recursive container types
+    py::bind_vector<RecursiveVector>(m, "RecursiveVector");
+    py::bind_map<RecursiveMap>(m, "RecursiveMap");
+    py::bind_map<MutuallyRecursiveContainerPairMV>(m, "MutuallyRecursiveContainerPairMV");
+    py::bind_vector<MutuallyRecursiveContainerPairVM>(m, "MutuallyRecursiveContainerPairVM");
+
     // The rest depends on numpy:
     try {
         py::module_::import("numpy");
diff --git a/wrap/pybind11/tests/test_stl_binders.py b/wrap/pybind11/tests/test_stl_binders.py
index d5e9ccced..e002f5b67 100644
--- a/wrap/pybind11/tests/test_stl_binders.py
+++ b/wrap/pybind11/tests/test_stl_binders.py
@@ -186,9 +186,9 @@ def test_map_string_double():
     um["ua"] = 1.1
     um["ub"] = 2.6
 
-    assert sorted(list(um)) == ["ua", "ub"]
+    assert sorted(um) == ["ua", "ub"]
     assert list(um.keys()) == list(um)
-    assert sorted(list(um.items())) == [("ua", 1.1), ("ub", 2.6)]
+    assert sorted(um.items()) == [("ua", 1.1), ("ub", 2.6)]
     assert list(zip(um.keys(), um.values())) == list(um.items())
     assert "UnorderedMapStringDouble" in str(um)
 
@@ -304,8 +304,52 @@ def test_map_delitem():
     um["ua"] = 1.1
     um["ub"] = 2.6
 
-    assert sorted(list(um)) == ["ua", "ub"]
-    assert sorted(list(um.items())) == [("ua", 1.1), ("ub", 2.6)]
+    assert sorted(um) == ["ua", "ub"]
+    assert sorted(um.items()) == [("ua", 1.1), ("ub", 2.6)]
     del um["ua"]
-    assert sorted(list(um)) == ["ub"]
-    assert sorted(list(um.items())) == [("ub", 2.6)]
+    assert sorted(um) == ["ub"]
+    assert sorted(um.items()) == [("ub", 2.6)]
+
+
+def test_map_view_types():
+    map_string_double = m.MapStringDouble()
+    unordered_map_string_double = m.UnorderedMapStringDouble()
+    map_string_double_const = m.MapStringDoubleConst()
+    unordered_map_string_double_const = m.UnorderedMapStringDoubleConst()
+
+    assert map_string_double.keys().__class__.__name__ == "KeysView[str]"
+    assert map_string_double.values().__class__.__name__ == "ValuesView[float]"
+    assert map_string_double.items().__class__.__name__ == "ItemsView[str, float]"
+
+    keys_type = type(map_string_double.keys())
+    assert type(unordered_map_string_double.keys()) is keys_type
+    assert type(map_string_double_const.keys()) is keys_type
+    assert type(unordered_map_string_double_const.keys()) is keys_type
+
+    values_type = type(map_string_double.values())
+    assert type(unordered_map_string_double.values()) is values_type
+    assert type(map_string_double_const.values()) is values_type
+    assert type(unordered_map_string_double_const.values()) is values_type
+
+    items_type = type(map_string_double.items())
+    assert type(unordered_map_string_double.items()) is items_type
+    assert type(map_string_double_const.items()) is items_type
+    assert type(unordered_map_string_double_const.items()) is items_type
+
+
+def test_recursive_vector():
+    recursive_vector = m.RecursiveVector()
+    recursive_vector.append(m.RecursiveVector())
+    recursive_vector[0].append(m.RecursiveVector())
+    recursive_vector[0].append(m.RecursiveVector())
+    # Can't use len() since test_stl_binders.cpp does not include stl.h,
+    # so the necessary conversion is missing
+    assert recursive_vector[0].count(m.RecursiveVector()) == 2
+
+
+def test_recursive_map():
+    recursive_map = m.RecursiveMap()
+    recursive_map[100] = m.RecursiveMap()
+    recursive_map[100][101] = m.RecursiveMap()
+    recursive_map[100][102] = m.RecursiveMap()
+    assert list(recursive_map[100].keys()) == [101, 102]
diff --git a/wrap/pybind11/tests/test_tagbased_polymorphic.cpp b/wrap/pybind11/tests/test_tagbased_polymorphic.cpp
index 2807e86ba..12ba6532f 100644
--- a/wrap/pybind11/tests/test_tagbased_polymorphic.cpp
+++ b/wrap/pybind11/tests/test_tagbased_polymorphic.cpp
@@ -117,7 +117,7 @@ std::string Animal::name_of_kind(Kind kind) {
     return raw_name;
 }
 
-namespace pybind11 {
+namespace PYBIND11_NAMESPACE {
 template <typename itype>
 struct polymorphic_type_hook<itype, detail::enable_if_t<std::is_base_of<Animal, itype>::value>> {
     static const void *get(const itype *src, const std::type_info *&type) {
@@ -125,7 +125,7 @@ struct polymorphic_type_hook<itype, detail::enable_if_t<std::is_base_of<Animal,
         return src;
     }
 };
-} // namespace pybind11
+} // namespace PYBIND11_NAMESPACE
 
 TEST_SUBMODULE(tagbased_polymorphic, m) {
     py::class_<Animal>(m, "Animal").def_readonly("name", &Animal::name);
diff --git a/wrap/pybind11/tests/test_type_caster_pyobject_ptr.cpp b/wrap/pybind11/tests/test_type_caster_pyobject_ptr.cpp
new file mode 100644
index 000000000..1667ea126
--- /dev/null
+++ b/wrap/pybind11/tests/test_type_caster_pyobject_ptr.cpp
@@ -0,0 +1,130 @@
+#include <pybind11/functional.h>
+#include <pybind11/stl.h>
+#include <pybind11/type_caster_pyobject_ptr.h>
+
+#include "pybind11_tests.h"
+
+#include <cstddef>
+#include <vector>
+
+namespace {
+
+std::vector<PyObject *> make_vector_pyobject_ptr(const py::object &ValueHolder) {
+    std::vector<PyObject *> vec_obj;
+    for (int i = 1; i < 3; i++) {
+        vec_obj.push_back(ValueHolder(i * 93).release().ptr());
+    }
+    // This vector now owns the refcounts.
+    return vec_obj;
+}
+
+} // namespace
+
+TEST_SUBMODULE(type_caster_pyobject_ptr, m) {
+    m.def("cast_from_pyobject_ptr", []() {
+        PyObject *ptr = PyLong_FromLongLong(6758L);
+        return py::cast(ptr, py::return_value_policy::take_ownership);
+    });
+    m.def("cast_handle_to_pyobject_ptr", [](py::handle obj) {
+        auto rc1 = obj.ref_count();
+        auto *ptr = py::cast<PyObject *>(obj);
+        auto rc2 = obj.ref_count();
+        if (rc2 != rc1 + 1) {
+            return -1;
+        }
+        return 100 - py::reinterpret_steal<py::object>(ptr).attr("value").cast<int>();
+    });
+    m.def("cast_object_to_pyobject_ptr", [](py::object obj) {
+        py::handle hdl = obj;
+        auto rc1 = hdl.ref_count();
+        auto *ptr = py::cast<PyObject *>(std::move(obj));
+        auto rc2 = hdl.ref_count();
+        if (rc2 != rc1) {
+            return -1;
+        }
+        return 300 - py::reinterpret_steal<py::object>(ptr).attr("value").cast<int>();
+    });
+    m.def("cast_list_to_pyobject_ptr", [](py::list lst) {
+        // This is to cover types implicitly convertible to object.
+        py::handle hdl = lst;
+        auto rc1 = hdl.ref_count();
+        auto *ptr = py::cast<PyObject *>(std::move(lst));
+        auto rc2 = hdl.ref_count();
+        if (rc2 != rc1) {
+            return -1;
+        }
+        return 400 - static_cast<int>(py::len(py::reinterpret_steal<py::list>(ptr)));
+    });
+
+    m.def(
+        "return_pyobject_ptr",
+        []() { return PyLong_FromLongLong(2314L); },
+        py::return_value_policy::take_ownership);
+    m.def("pass_pyobject_ptr", [](PyObject *ptr) {
+        return 200 - py::reinterpret_borrow<py::object>(ptr).attr("value").cast<int>();
+    });
+
+    m.def("call_callback_with_object_return",
+          [](const std::function<py::object(int)> &cb, int value) { return cb(value); });
+    m.def(
+        "call_callback_with_pyobject_ptr_return",
+        [](const std::function<PyObject *(int)> &cb, int value) { return cb(value); },
+        py::return_value_policy::take_ownership);
+    m.def(
+        "call_callback_with_pyobject_ptr_arg",
+        [](const std::function<int(PyObject *)> &cb, py::handle obj) { return cb(obj.ptr()); },
+        py::arg("cb"), // This triggers return_value_policy::automatic_reference
+        py::arg("obj"));
+
+    m.def("cast_to_pyobject_ptr_nullptr", [](bool set_error) {
+        if (set_error) {
+            PyErr_SetString(PyExc_RuntimeError, "Reflective of healthy error handling.");
+        }
+        PyObject *ptr = nullptr;
+        py::cast(ptr);
+    });
+
+    m.def("cast_to_pyobject_ptr_non_nullptr_with_error_set", []() {
+        PyErr_SetString(PyExc_RuntimeError, "Reflective of unhealthy error handling.");
+        py::cast(Py_None);
+    });
+
+    m.def("pass_list_pyobject_ptr", [](const std::vector<PyObject *> &vec_obj) {
+        int acc = 0;
+        for (const auto &ptr : vec_obj) {
+            acc = acc * 1000 + py::reinterpret_borrow<py::object>(ptr).attr("value").cast<int>();
+        }
+        return acc;
+    });
+
+    m.def("return_list_pyobject_ptr_take_ownership",
+          make_vector_pyobject_ptr,
+          // Ownership is transferred one-by-one when the vector is converted to a Python list.
+          py::return_value_policy::take_ownership);
+
+    m.def("return_list_pyobject_ptr_reference",
+          make_vector_pyobject_ptr,
+          // Ownership is not transferred.
+          py::return_value_policy::reference);
+
+    m.def("dec_ref_each_pyobject_ptr", [](const std::vector<PyObject *> &vec_obj) {
+        std::size_t i = 0;
+        for (; i < vec_obj.size(); i++) {
+            py::handle h(vec_obj[i]);
+            if (static_cast<std::size_t>(h.ref_count()) < 2) {
+                break; // Something is badly wrong.
+            }
+            h.dec_ref();
+        }
+        return i;
+    });
+
+    m.def("pass_pyobject_ptr_and_int", [](PyObject *, int) {});
+
+#ifdef PYBIND11_NO_COMPILE_SECTION // Change to ifndef for manual testing.
+    {
+        PyObject *ptr = nullptr;
+        (void) py::cast(*ptr);
+    }
+#endif
+}
diff --git a/wrap/pybind11/tests/test_type_caster_pyobject_ptr.py b/wrap/pybind11/tests/test_type_caster_pyobject_ptr.py
new file mode 100644
index 000000000..1f1ece2ba
--- /dev/null
+++ b/wrap/pybind11/tests/test_type_caster_pyobject_ptr.py
@@ -0,0 +1,104 @@
+import pytest
+
+from pybind11_tests import type_caster_pyobject_ptr as m
+
+
+# For use as a temporary user-defined object, to maximize sensitivity of the tests below.
+class ValueHolder:
+    def __init__(self, value):
+        self.value = value
+
+
+def test_cast_from_pyobject_ptr():
+    assert m.cast_from_pyobject_ptr() == 6758
+
+
+def test_cast_handle_to_pyobject_ptr():
+    assert m.cast_handle_to_pyobject_ptr(ValueHolder(24)) == 76
+
+
+def test_cast_object_to_pyobject_ptr():
+    assert m.cast_object_to_pyobject_ptr(ValueHolder(43)) == 257
+
+
+def test_cast_list_to_pyobject_ptr():
+    assert m.cast_list_to_pyobject_ptr([1, 2, 3, 4, 5]) == 395
+
+
+def test_return_pyobject_ptr():
+    assert m.return_pyobject_ptr() == 2314
+
+
+def test_pass_pyobject_ptr():
+    assert m.pass_pyobject_ptr(ValueHolder(82)) == 118
+
+
+@pytest.mark.parametrize(
+    "call_callback",
+    [
+        m.call_callback_with_object_return,
+        m.call_callback_with_pyobject_ptr_return,
+    ],
+)
+def test_call_callback_with_object_return(call_callback):
+    def cb(value):
+        if value < 0:
+            raise ValueError("Raised from cb")
+        return ValueHolder(1000 - value)
+
+    assert call_callback(cb, 287).value == 713
+
+    with pytest.raises(ValueError, match="^Raised from cb$"):
+        call_callback(cb, -1)
+
+
+def test_call_callback_with_pyobject_ptr_arg():
+    def cb(obj):
+        return 300 - obj.value
+
+    assert m.call_callback_with_pyobject_ptr_arg(cb, ValueHolder(39)) == 261
+
+
+@pytest.mark.parametrize("set_error", [True, False])
+def test_cast_to_python_nullptr(set_error):
+    expected = {
+        True: r"^Reflective of healthy error handling\.$",
+        False: (
+            r"^Internal error: pybind11::error_already_set called "
+            r"while Python error indicator not set\.$"
+        ),
+    }[set_error]
+    with pytest.raises(RuntimeError, match=expected):
+        m.cast_to_pyobject_ptr_nullptr(set_error)
+
+
+def test_cast_to_python_non_nullptr_with_error_set():
+    with pytest.raises(SystemError) as excinfo:
+        m.cast_to_pyobject_ptr_non_nullptr_with_error_set()
+    assert str(excinfo.value) == "src != nullptr but PyErr_Occurred()"
+    assert str(excinfo.value.__cause__) == "Reflective of unhealthy error handling."
+
+
+def test_pass_list_pyobject_ptr():
+    acc = m.pass_list_pyobject_ptr([ValueHolder(842), ValueHolder(452)])
+    assert acc == 842452
+
+
+def test_return_list_pyobject_ptr_take_ownership():
+    vec_obj = m.return_list_pyobject_ptr_take_ownership(ValueHolder)
+    assert [e.value for e in vec_obj] == [93, 186]
+
+
+def test_return_list_pyobject_ptr_reference():
+    vec_obj = m.return_list_pyobject_ptr_reference(ValueHolder)
+    assert [e.value for e in vec_obj] == [93, 186]
+    # Commenting out the next `assert` will leak the Python references.
+    # An easy way to see evidence of the leaks:
+    # Insert `while True:` as the first line of this function and monitor the
+    # process RES (Resident Memory Size) with the Unix top command.
+    assert m.dec_ref_each_pyobject_ptr(vec_obj) == 2
+
+
+def test_type_caster_name_via_incompatible_function_arguments_type_error():
+    with pytest.raises(TypeError, match=r"1\. \(arg0: object, arg1: int\) -> None"):
+        m.pass_pyobject_ptr_and_int(ValueHolder(101), ValueHolder(202))
diff --git a/wrap/pybind11/tests/test_unnamed_namespace_a.cpp b/wrap/pybind11/tests/test_unnamed_namespace_a.cpp
new file mode 100644
index 000000000..2152e64bd
--- /dev/null
+++ b/wrap/pybind11/tests/test_unnamed_namespace_a.cpp
@@ -0,0 +1,38 @@
+#include "pybind11_tests.h"
+
+namespace {
+struct any_struct {};
+} // namespace
+
+TEST_SUBMODULE(unnamed_namespace_a, m) {
+    if (py::detail::get_type_info(typeid(any_struct)) == nullptr) {
+        py::class_<any_struct>(m, "unnamed_namespace_a_any_struct");
+    } else {
+        m.attr("unnamed_namespace_a_any_struct") = py::none();
+    }
+    m.attr("PYBIND11_INTERNALS_VERSION") = PYBIND11_INTERNALS_VERSION;
+    m.attr("defined_WIN32_or__WIN32") =
+#if defined(WIN32) || defined(_WIN32)
+        true;
+#else
+        false;
+#endif
+    m.attr("defined___clang__") =
+#if defined(__clang__)
+        true;
+#else
+        false;
+#endif
+    m.attr("defined__LIBCPP_VERSION") =
+#if defined(_LIBCPP_VERSION)
+        true;
+#else
+        false;
+#endif
+    m.attr("defined___GLIBCXX__") =
+#if defined(__GLIBCXX__)
+        true;
+#else
+        false;
+#endif
+}
diff --git a/wrap/pybind11/tests/test_unnamed_namespace_a.py b/wrap/pybind11/tests/test_unnamed_namespace_a.py
new file mode 100644
index 000000000..9d9856c5a
--- /dev/null
+++ b/wrap/pybind11/tests/test_unnamed_namespace_a.py
@@ -0,0 +1,34 @@
+import pytest
+
+from pybind11_tests import unnamed_namespace_a as m
+from pybind11_tests import unnamed_namespace_b as mb
+
+XFAIL_CONDITION = (
+    "(m.PYBIND11_INTERNALS_VERSION <= 4 and (m.defined___clang__ or not m.defined___GLIBCXX__))"
+    " or "
+    "(m.PYBIND11_INTERNALS_VERSION >= 5 and not m.defined_WIN32_or__WIN32"
+    " and "
+    "(m.defined___clang__ or m.defined__LIBCPP_VERSION))"
+)
+XFAIL_REASON = "Known issues: https://github.com/pybind/pybind11/pull/4319"
+
+
+@pytest.mark.xfail(XFAIL_CONDITION, reason=XFAIL_REASON, strict=False)
+@pytest.mark.parametrize(
+    "any_struct", [m.unnamed_namespace_a_any_struct, mb.unnamed_namespace_b_any_struct]
+)
+def test_have_class_any_struct(any_struct):
+    assert any_struct is not None
+
+
+def test_have_at_least_one_class_any_struct():
+    assert (
+        m.unnamed_namespace_a_any_struct is not None
+        or mb.unnamed_namespace_b_any_struct is not None
+    )
+
+
+@pytest.mark.xfail(XFAIL_CONDITION, reason=XFAIL_REASON, strict=True)
+def test_have_both_class_any_struct():
+    assert m.unnamed_namespace_a_any_struct is not None
+    assert mb.unnamed_namespace_b_any_struct is not None
diff --git a/wrap/pybind11/tests/test_unnamed_namespace_b.cpp b/wrap/pybind11/tests/test_unnamed_namespace_b.cpp
new file mode 100644
index 000000000..f97757a7d
--- /dev/null
+++ b/wrap/pybind11/tests/test_unnamed_namespace_b.cpp
@@ -0,0 +1,13 @@
+#include "pybind11_tests.h"
+
+namespace {
+struct any_struct {};
+} // namespace
+
+TEST_SUBMODULE(unnamed_namespace_b, m) {
+    if (py::detail::get_type_info(typeid(any_struct)) == nullptr) {
+        py::class_<any_struct>(m, "unnamed_namespace_b_any_struct");
+    } else {
+        m.attr("unnamed_namespace_b_any_struct") = py::none();
+    }
+}
diff --git a/wrap/pybind11/tests/test_unnamed_namespace_b.py b/wrap/pybind11/tests/test_unnamed_namespace_b.py
new file mode 100644
index 000000000..4bcaa7a6c
--- /dev/null
+++ b/wrap/pybind11/tests/test_unnamed_namespace_b.py
@@ -0,0 +1,5 @@
+from pybind11_tests import unnamed_namespace_b as m
+
+
+def test_have_attr_any_struct():
+    assert hasattr(m, "unnamed_namespace_b_any_struct")
diff --git a/wrap/pybind11/tests/test_vector_unique_ptr_member.cpp b/wrap/pybind11/tests/test_vector_unique_ptr_member.cpp
new file mode 100644
index 000000000..680cf9a6d
--- /dev/null
+++ b/wrap/pybind11/tests/test_vector_unique_ptr_member.cpp
@@ -0,0 +1,54 @@
+#include "pybind11_tests.h"
+
+#include <cstddef>
+#include <memory>
+#include <vector>
+
+namespace pybind11_tests {
+namespace vector_unique_ptr_member {
+
+struct DataType {};
+
+// Reduced from a use case in the wild.
+struct VectorOwner {
+    static std::unique_ptr<VectorOwner> Create(std::size_t num_elems) {
+        return std::unique_ptr<VectorOwner>(
+            new VectorOwner(std::vector<std::unique_ptr<DataType>>(num_elems)));
+    }
+
+    std::size_t data_size() const { return data_.size(); }
+
+private:
+    explicit VectorOwner(std::vector<std::unique_ptr<DataType>> data) : data_(std::move(data)) {}
+
+    const std::vector<std::unique_ptr<DataType>> data_;
+};
+
+} // namespace vector_unique_ptr_member
+} // namespace pybind11_tests
+
+namespace pybind11 {
+namespace detail {
+
+template <>
+struct is_copy_constructible<pybind11_tests::vector_unique_ptr_member::VectorOwner>
+    : std::false_type {};
+
+template <>
+struct is_move_constructible<pybind11_tests::vector_unique_ptr_member::VectorOwner>
+    : std::false_type {};
+
+} // namespace detail
+} // namespace pybind11
+
+using namespace pybind11_tests::vector_unique_ptr_member;
+
+py::object py_cast_VectorOwner_ptr(VectorOwner *ptr) { return py::cast(ptr); }
+
+TEST_SUBMODULE(vector_unique_ptr_member, m) {
+    py::class_<VectorOwner>(m, "VectorOwner")
+        .def_static("Create", &VectorOwner::Create)
+        .def("data_size", &VectorOwner::data_size);
+
+    m.def("py_cast_VectorOwner_ptr", py_cast_VectorOwner_ptr);
+}
diff --git a/wrap/pybind11/tests/test_vector_unique_ptr_member.py b/wrap/pybind11/tests/test_vector_unique_ptr_member.py
new file mode 100644
index 000000000..2da3d97c3
--- /dev/null
+++ b/wrap/pybind11/tests/test_vector_unique_ptr_member.py
@@ -0,0 +1,14 @@
+import pytest
+
+from pybind11_tests import vector_unique_ptr_member as m
+
+
+@pytest.mark.parametrize("num_elems", range(3))
+def test_create(num_elems):
+    vo = m.VectorOwner.Create(num_elems)
+    assert vo.data_size() == num_elems
+
+
+def test_cast():
+    vo = m.VectorOwner.Create(0)
+    assert m.py_cast_VectorOwner_ptr(vo) is vo
diff --git a/wrap/pybind11/tests/test_virtual_functions.cpp b/wrap/pybind11/tests/test_virtual_functions.cpp
index 323aa0d22..93b136ad3 100644
--- a/wrap/pybind11/tests/test_virtual_functions.cpp
+++ b/wrap/pybind11/tests/test_virtual_functions.cpp
@@ -173,7 +173,8 @@ struct AdderBase {
     using DataVisitor = std::function<void(const Data &)>;
 
     virtual void
-    operator()(const Data &first, const Data &second, const DataVisitor &visitor) const = 0;
+    operator()(const Data &first, const Data &second, const DataVisitor &visitor) const
+        = 0;
     virtual ~AdderBase() = default;
     AdderBase() = default;
     AdderBase(const AdderBase &) = delete;
diff --git a/wrap/pybind11/tests/test_virtual_functions.py b/wrap/pybind11/tests/test_virtual_functions.py
index 4d00d3690..c17af7df5 100644
--- a/wrap/pybind11/tests/test_virtual_functions.py
+++ b/wrap/pybind11/tests/test_virtual_functions.py
@@ -192,8 +192,7 @@ def test_move_support():
     class NCVirtExt(m.NCVirt):
         def get_noncopyable(self, a, b):
             # Constructs and returns a new instance:
-            nc = m.NonCopyable(a * a, b * b)
-            return nc
+            return m.NonCopyable(a * a, b * b)
 
         def get_movable(self, a, b):
             # Return a referenced copy
@@ -256,7 +255,7 @@ def test_dispatch_issue(msg):
     assert m.dispatch_issue_go(b) == "Yay.."
 
 
-def test_recursive_dispatch_issue(msg):
+def test_recursive_dispatch_issue():
     """#3357: Recursive dispatch fails to find python function override"""
 
     class Data(m.Data):
@@ -269,7 +268,7 @@ def test_recursive_dispatch_issue(msg):
             # lambda is a workaround, which adds extra frame to the
             # current CPython thread. Removing lambda reveals the bug
             # [https://github.com/pybind/pybind11/issues/3357]
-            (lambda: visitor(Data(first.value + second.value)))()
+            (lambda: visitor(Data(first.value + second.value)))()  # noqa: PLC3002
 
     class StoreResultVisitor:
         def __init__(self):
diff --git a/wrap/pybind11/tools/FindCatch.cmake b/wrap/pybind11/tools/FindCatch.cmake
index 57bba58b3..5d3fcbfb1 100644
--- a/wrap/pybind11/tools/FindCatch.cmake
+++ b/wrap/pybind11/tools/FindCatch.cmake
@@ -36,10 +36,14 @@ endfunction()
 function(_download_catch version destination_dir)
   message(STATUS "Downloading catch v${version}...")
   set(url https://github.com/philsquared/Catch/releases/download/v${version}/catch.hpp)
-  file(DOWNLOAD ${url} "${destination_dir}/catch.hpp" STATUS status)
+  file(
+    DOWNLOAD ${url} "${destination_dir}/catch.hpp"
+    STATUS status
+    LOG log)
   list(GET status 0 error)
   if(error)
-    message(FATAL_ERROR "Could not download ${url}")
+    string(REPLACE "\n" "\n  " log "  ${log}")
+    message(FATAL_ERROR "Could not download URL:\n" "  ${url}\n" "Log:\n" "${log}")
   endif()
   set(CATCH_INCLUDE_DIR
       "${destination_dir}"
diff --git a/wrap/pybind11/tools/FindPythonLibsNew.cmake b/wrap/pybind11/tools/FindPythonLibsNew.cmake
index a5a628fd7..ce558d4ec 100644
--- a/wrap/pybind11/tools/FindPythonLibsNew.cmake
+++ b/wrap/pybind11/tools/FindPythonLibsNew.cmake
@@ -151,9 +151,13 @@ if(NOT _PYTHON_SUCCESS MATCHES 0)
   return()
 endif()
 
+option(
+  PYBIND11_PYTHONLIBS_OVERWRITE
+  "Overwrite cached values read from Python library (classic search). Turn off if cross-compiling and manually setting these values."
+  ON)
 # Can manually set values when cross-compiling
 macro(_PYBIND11_GET_IF_UNDEF lst index name)
-  if(NOT DEFINED "${name}")
+  if(PYBIND11_PYTHONLIBS_OVERWRITE OR NOT DEFINED "${name}")
     list(GET "${lst}" "${index}" "${name}")
   endif()
 endmacro()
@@ -204,7 +208,9 @@ string(REGEX REPLACE "\\\\" "/" PYTHON_PREFIX "${PYTHON_PREFIX}")
 string(REGEX REPLACE "\\\\" "/" PYTHON_INCLUDE_DIR "${PYTHON_INCLUDE_DIR}")
 string(REGEX REPLACE "\\\\" "/" PYTHON_SITE_PACKAGES "${PYTHON_SITE_PACKAGES}")
 
-if(CMAKE_HOST_WIN32)
+if(DEFINED PYTHON_LIBRARY)
+  # Don't write to PYTHON_LIBRARY if it's already set
+elseif(CMAKE_HOST_WIN32)
   set(PYTHON_LIBRARY "${PYTHON_PREFIX}/libs/python${PYTHON_LIBRARY_SUFFIX}.lib")
 
   # when run in a venv, PYTHON_PREFIX points to it. But the libraries remain in the
@@ -270,7 +276,7 @@ if(NOT PYTHON_DEBUG_LIBRARY)
 endif()
 set(PYTHON_DEBUG_LIBRARIES "${PYTHON_DEBUG_LIBRARY}")
 
-find_package_message(PYTHON "Found PythonLibs: ${PYTHON_LIBRARY}"
+find_package_message(PYTHON "Found PythonLibs: ${PYTHON_LIBRARIES}"
                      "${PYTHON_EXECUTABLE}${PYTHON_VERSION_STRING}")
 
 set(PYTHONLIBS_FOUND TRUE)
diff --git a/wrap/pybind11/tools/JoinPaths.cmake b/wrap/pybind11/tools/JoinPaths.cmake
new file mode 100644
index 000000000..c68d91b84
--- /dev/null
+++ b/wrap/pybind11/tools/JoinPaths.cmake
@@ -0,0 +1,23 @@
+# This module provides function for joining paths
+# known from most languages
+#
+# SPDX-License-Identifier: (MIT OR CC0-1.0)
+# Copyright 2020 Jan Tojnar
+# https://github.com/jtojnar/cmake-snips
+#
+# Modelled after Python’s os.path.join
+# https://docs.python.org/3.7/library/os.path.html#os.path.join
+# Windows not supported
+function(join_paths joined_path first_path_segment)
+    set(temp_path "${first_path_segment}")
+    foreach(current_segment IN LISTS ARGN)
+        if(NOT ("${current_segment}" STREQUAL ""))
+            if(IS_ABSOLUTE "${current_segment}")
+                set(temp_path "${current_segment}")
+            else()
+                set(temp_path "${temp_path}/${current_segment}")
+            endif()
+        endif()
+    endforeach()
+    set(${joined_path} "${temp_path}" PARENT_SCOPE)
+endfunction()
diff --git a/wrap/pybind11/tools/codespell_ignore_lines_from_errors.py b/wrap/pybind11/tools/codespell_ignore_lines_from_errors.py
new file mode 100644
index 000000000..4ec9add12
--- /dev/null
+++ b/wrap/pybind11/tools/codespell_ignore_lines_from_errors.py
@@ -0,0 +1,39 @@
+"""Simple script for rebuilding .codespell-ignore-lines
+
+Usage:
+
+cat < /dev/null > .codespell-ignore-lines
+pre-commit run --all-files codespell >& /tmp/codespell_errors.txt
+python3 tools/codespell_ignore_lines_from_errors.py /tmp/codespell_errors.txt > .codespell-ignore-lines
+
+git diff to review changes, then commit, push.
+"""
+
+import sys
+from typing import List
+
+
+def run(args: List[str]) -> None:
+    assert len(args) == 1, "codespell_errors.txt"
+    cache = {}
+    done = set()
+    with open(args[0]) as f:
+        lines = f.read().splitlines()
+
+    for line in sorted(lines):
+        i = line.find(" ==> ")
+        if i > 0:
+            flds = line[:i].split(":")
+            if len(flds) >= 2:
+                filename, line_num = flds[:2]
+                if filename not in cache:
+                    with open(filename) as f:
+                        cache[filename] = f.read().splitlines()
+                supp = cache[filename][int(line_num) - 1]
+                if supp not in done:
+                    print(supp)
+                    done.add(supp)
+
+
+if __name__ == "__main__":
+    run(args=sys.argv[1:])
diff --git a/wrap/pybind11/tools/make_changelog.py b/wrap/pybind11/tools/make_changelog.py
index 839040a93..b5bd83294 100755
--- a/wrap/pybind11/tools/make_changelog.py
+++ b/wrap/pybind11/tools/make_changelog.py
@@ -31,8 +31,10 @@ issues = (issue for page in issues_pages for issue in page)
 missing = []
 
 for issue in issues:
-    changelog = ENTRY.findall(issue.body)
-    if changelog:
+    changelog = ENTRY.findall(issue.body or "")
+    if not changelog or not changelog[0]:
+        missing.append(issue)
+    else:
         (msg,) = changelog
         if not msg.startswith("* "):
             msg = "* " + msg
@@ -44,9 +46,6 @@ for issue in issues:
         print(Syntax(msg, "rst", theme="ansi_light", word_wrap=True))
         print()
 
-    else:
-        missing.append(issue)
-
 if missing:
     print()
     print("[blue]" + "-" * 30)
diff --git a/wrap/pybind11/tools/pybind11.pc.in b/wrap/pybind11/tools/pybind11.pc.in
new file mode 100644
index 000000000..402f0b357
--- /dev/null
+++ b/wrap/pybind11/tools/pybind11.pc.in
@@ -0,0 +1,7 @@
+prefix=@prefix_for_pc_file@
+includedir=@includedir_for_pc_file@
+
+Name: @PROJECT_NAME@
+Description: Seamless operability between C++11 and Python
+Version: @PROJECT_VERSION@
+Cflags: -I${includedir}
diff --git a/wrap/pybind11/tools/pybind11Common.cmake b/wrap/pybind11/tools/pybind11Common.cmake
index e1fb601ac..308d1b70d 100644
--- a/wrap/pybind11/tools/pybind11Common.cmake
+++ b/wrap/pybind11/tools/pybind11Common.cmake
@@ -5,8 +5,8 @@ Adds the following targets::
     pybind11::pybind11 - link to headers and pybind11
     pybind11::module - Adds module links
     pybind11::embed - Adds embed links
-    pybind11::lto - Link time optimizations (manual selection)
-    pybind11::thin_lto - Link time optimizations (manual selection)
+    pybind11::lto - Link time optimizations (only if CMAKE_INTERPROCEDURAL_OPTIMIZATION is not set)
+    pybind11::thin_lto - Link time optimizations (only if CMAKE_INTERPROCEDURAL_OPTIMIZATION is not set)
     pybind11::python_link_helper - Adds link to Python libraries
     pybind11::windows_extras - MSVC bigobj and mp for building multithreaded
     pybind11::opt_size - avoid optimizations that increase code size
@@ -20,7 +20,7 @@ Adds the following functions::
 
 # CMake 3.10 has an include_guard command, but we can't use that yet
 # include_guard(global) (pre-CMake 3.10)
-if(TARGET pybind11::lto)
+if(TARGET pybind11::pybind11)
   return()
 endif()
 
@@ -163,11 +163,19 @@ endif()
 
 # --------------------- Python specifics -------------------------
 
+# CMake 3.27 removes the classic FindPythonInterp if CMP0148 is NEW
+if(CMAKE_VERSION VERSION_LESS "3.27")
+  set(_pybind11_missing_old_python "OLD")
+else()
+  cmake_policy(GET CMP0148 _pybind11_missing_old_python)
+endif()
+
 # Check to see which Python mode we are in, new, old, or no python
 if(PYBIND11_NOPYTHON)
   set(_pybind11_nopython ON)
 elseif(
-  PYBIND11_FINDPYTHON
+  _pybind11_missing_old_python STREQUAL "NEW"
+  OR PYBIND11_FINDPYTHON
   OR Python_FOUND
   OR Python2_FOUND
   OR Python3_FOUND)
@@ -311,6 +319,16 @@ function(_pybind11_generate_lto target prefer_thin_lto)
         HAS_FLTO "-flto${cxx_append}" "-flto${linker_append}" PYBIND11_LTO_CXX_FLAGS
         PYBIND11_LTO_LINKER_FLAGS)
     endif()
+  elseif(CMAKE_CXX_COMPILER_ID MATCHES "IntelLLVM")
+    # IntelLLVM equivalent to LTO is called IPO; also IntelLLVM is WIN32/UNIX
+    # WARNING/HELP WANTED: This block of code is currently not covered by pybind11 GitHub Actions!
+    if(WIN32)
+      _pybind11_return_if_cxx_and_linker_flags_work(
+        HAS_INTEL_IPO "-Qipo" "-Qipo" PYBIND11_LTO_CXX_FLAGS PYBIND11_LTO_LINKER_FLAGS)
+    else()
+      _pybind11_return_if_cxx_and_linker_flags_work(
+        HAS_INTEL_IPO "-ipo" "-ipo" PYBIND11_LTO_CXX_FLAGS PYBIND11_LTO_LINKER_FLAGS)
+    endif()
   elseif(CMAKE_CXX_COMPILER_ID MATCHES "Intel")
     # Intel equivalent to LTO is called IPO
     _pybind11_return_if_cxx_and_linker_flags_work(HAS_INTEL_IPO "-ipo" "-ipo"
@@ -362,11 +380,13 @@ function(_pybind11_generate_lto target prefer_thin_lto)
   endif()
 endfunction()
 
-add_library(pybind11::lto IMPORTED INTERFACE ${optional_global})
-_pybind11_generate_lto(pybind11::lto FALSE)
+if(NOT DEFINED CMAKE_INTERPROCEDURAL_OPTIMIZATION)
+  add_library(pybind11::lto IMPORTED INTERFACE ${optional_global})
+  _pybind11_generate_lto(pybind11::lto FALSE)
 
-add_library(pybind11::thin_lto IMPORTED INTERFACE ${optional_global})
-_pybind11_generate_lto(pybind11::thin_lto TRUE)
+  add_library(pybind11::thin_lto IMPORTED INTERFACE ${optional_global})
+  _pybind11_generate_lto(pybind11::thin_lto TRUE)
+endif()
 
 # ---------------------- pybind11_strip -----------------------------
 
diff --git a/wrap/pybind11/tools/pybind11Config.cmake.in b/wrap/pybind11/tools/pybind11Config.cmake.in
index 9383e8c67..5734f437b 100644
--- a/wrap/pybind11/tools/pybind11Config.cmake.in
+++ b/wrap/pybind11/tools/pybind11Config.cmake.in
@@ -63,7 +63,9 @@ Modes
 
 There are two modes provided; classic, which is built on the old Python
 discovery packages in CMake, or the new FindPython mode, which uses FindPython
-from 3.12+ forward (3.15+ _highly_ recommended).
+from 3.12+ forward (3.15+ _highly_ recommended). If you set the minimum or
+maximum version of CMake to 3.27+, then FindPython is the default (since
+FindPythonInterp/FindPythonLibs has been removed via policy `CMP0148`).
 
 New FindPython mode
 ^^^^^^^^^^^^^^^^^^^
diff --git a/wrap/pybind11/tools/pybind11NewTools.cmake b/wrap/pybind11/tools/pybind11NewTools.cmake
index abba0fe0e..7d7424a79 100644
--- a/wrap/pybind11/tools/pybind11NewTools.cmake
+++ b/wrap/pybind11/tools/pybind11NewTools.cmake
@@ -9,7 +9,7 @@ if(CMAKE_VERSION VERSION_LESS 3.12)
   message(FATAL_ERROR "You cannot use the new FindPython module with CMake < 3.12")
 endif()
 
-include_guard(GLOBAL)
+include_guard(DIRECTORY)
 
 get_property(
   is_config
@@ -233,7 +233,9 @@ function(pybind11_add_module target_name)
     endif()
   endif()
 
-  if(NOT MSVC AND NOT ${CMAKE_BUILD_TYPE} MATCHES Debug|RelWithDebInfo)
+  # Use case-insensitive comparison to match the result of $<CONFIG:cfgs>
+  string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
+  if(NOT MSVC AND NOT "${uppercase_CMAKE_BUILD_TYPE}" MATCHES DEBUG|RELWITHDEBINFO)
     # Strip unnecessary sections of the binary on Linux/macOS
     pybind11_strip(${target_name})
   endif()
diff --git a/wrap/pybind11/tools/pybind11Tools.cmake b/wrap/pybind11/tools/pybind11Tools.cmake
index 5535e872f..66ad00a47 100644
--- a/wrap/pybind11/tools/pybind11Tools.cmake
+++ b/wrap/pybind11/tools/pybind11Tools.cmake
@@ -115,6 +115,7 @@ if(PYTHON_IS_DEBUG)
     PROPERTY INTERFACE_COMPILE_DEFINITIONS Py_DEBUG)
 endif()
 
+# The <3.11 code here does not support release/debug builds at the same time, like on vcpkg
 if(CMAKE_VERSION VERSION_LESS 3.11)
   set_property(
     TARGET pybind11::module
@@ -130,16 +131,19 @@ if(CMAKE_VERSION VERSION_LESS 3.11)
     APPEND
     PROPERTY INTERFACE_LINK_LIBRARIES pybind11::pybind11 $<BUILD_INTERFACE:${PYTHON_LIBRARIES}>)
 else()
+  # The IMPORTED INTERFACE library here is to ensure that "debug" and "release" get processed outside
+  # of a generator expression - https://gitlab.kitware.com/cmake/cmake/-/issues/18424, as they are
+  # target_link_library keywords rather than real libraries.
+  add_library(pybind11::_ClassicPythonLibraries IMPORTED INTERFACE)
+  target_link_libraries(pybind11::_ClassicPythonLibraries INTERFACE ${PYTHON_LIBRARIES})
   target_link_libraries(
     pybind11::module
     INTERFACE
       pybind11::python_link_helper
-      "$<$<OR:$<PLATFORM_ID:Windows>,$<PLATFORM_ID:Cygwin>>:$<BUILD_INTERFACE:${PYTHON_LIBRARIES}>>"
-  )
+      "$<$<OR:$<PLATFORM_ID:Windows>,$<PLATFORM_ID:Cygwin>>:pybind11::_ClassicPythonLibraries>")
 
   target_link_libraries(pybind11::embed INTERFACE pybind11::pybind11
-                                                  $<BUILD_INTERFACE:${PYTHON_LIBRARIES}>)
-
+                                                  pybind11::_ClassicPythonLibraries)
 endif()
 
 function(pybind11_extension name)
@@ -208,7 +212,9 @@ function(pybind11_add_module target_name)
     endif()
   endif()
 
-  if(NOT MSVC AND NOT ${CMAKE_BUILD_TYPE} MATCHES Debug|RelWithDebInfo)
+  # Use case-insensitive comparison to match the result of $<CONFIG:cfgs>
+  string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
+  if(NOT MSVC AND NOT "${uppercase_CMAKE_BUILD_TYPE}" MATCHES DEBUG|RELWITHDEBINFO)
     pybind11_strip(${target_name})
   endif()
 
diff --git a/wrap/pybind11/tools/setup_global.py.in b/wrap/pybind11/tools/setup_global.py.in
index 8aa387178..885ac5c72 100644
--- a/wrap/pybind11/tools/setup_global.py.in
+++ b/wrap/pybind11/tools/setup_global.py.in
@@ -27,9 +27,11 @@ class InstallHeadersNested(install_headers):
 
 main_headers = glob.glob("pybind11/include/pybind11/*.h")
 detail_headers = glob.glob("pybind11/include/pybind11/detail/*.h")
+eigen_headers = glob.glob("pybind11/include/pybind11/eigen/*.h")
 stl_headers = glob.glob("pybind11/include/pybind11/stl/*.h")
 cmake_files = glob.glob("pybind11/share/cmake/pybind11/*.cmake")
-headers = main_headers + detail_headers + stl_headers
+pkgconfig_files = glob.glob("pybind11/share/pkgconfig/*.pc")
+headers = main_headers + detail_headers + stl_headers + eigen_headers
 
 cmdclass = {"install_headers": InstallHeadersNested}
 $extra_cmd
@@ -51,8 +53,10 @@ setup(
     headers=headers,
     data_files=[
         (base + "share/cmake/pybind11", cmake_files),
+        (base + "share/pkgconfig", pkgconfig_files),
         (base + "include/pybind11", main_headers),
         (base + "include/pybind11/detail", detail_headers),
+        (base + "include/pybind11/eigen", eigen_headers),
         (base + "include/pybind11/stl", stl_headers),
     ],
     cmdclass=cmdclass,
diff --git a/wrap/pybind11/tools/setup_main.py.in b/wrap/pybind11/tools/setup_main.py.in
index 738d73faa..6358cc7b9 100644
--- a/wrap/pybind11/tools/setup_main.py.in
+++ b/wrap/pybind11/tools/setup_main.py.in
@@ -15,15 +15,19 @@ setup(
         "pybind11",
         "pybind11.include.pybind11",
         "pybind11.include.pybind11.detail",
+        "pybind11.include.pybind11.eigen",
         "pybind11.include.pybind11.stl",
         "pybind11.share.cmake.pybind11",
+        "pybind11.share.pkgconfig",
     ],
     package_data={
         "pybind11": ["py.typed"],
         "pybind11.include.pybind11": ["*.h"],
         "pybind11.include.pybind11.detail": ["*.h"],
+        "pybind11.include.pybind11.eigen": ["*.h"],
         "pybind11.include.pybind11.stl": ["*.h"],
         "pybind11.share.cmake.pybind11": ["*.cmake"],
+        "pybind11.share.pkgconfig": ["*.pc"],
     },
     extras_require={
         "global": ["pybind11_global==$version"]