diff --git a/gtsam_unstable/discrete/AllDiff.cpp b/gtsam_unstable/discrete/AllDiff.cpp
index bff524bc2..cf598b3f4 100644
--- a/gtsam_unstable/discrete/AllDiff.cpp
+++ b/gtsam_unstable/discrete/AllDiff.cpp
@@ -10,6 +10,7 @@
 #include <gtsam_unstable/discrete/Domain.h>
 
 #include <boost/make_shared.hpp>
+#include <optional>
 
 namespace gtsam {
 
@@ -64,7 +65,7 @@ bool AllDiff::ensureArcConsistency(Key j, Domains* domains) const {
   // a value in domains->at(j) that does not occur in any other connected domain.
   // If found, we make this a singleton...
   // TODO: make a new constraint where this really is true
-  boost::optional<Domain> maybeChanged = Dj.checkAllDiff(keys_, *domains);
+  std::optional<Domain> maybeChanged = Dj.checkAllDiff(keys_, *domains);
   if (maybeChanged) {
     Dj = *maybeChanged;
     return true;
diff --git a/gtsam_unstable/discrete/Domain.cpp b/gtsam_unstable/discrete/Domain.cpp
index cf0da42e7..f2b7d9f95 100644
--- a/gtsam_unstable/discrete/Domain.cpp
+++ b/gtsam_unstable/discrete/Domain.cpp
@@ -61,7 +61,7 @@ bool Domain::ensureArcConsistency(Key j, Domains* domains) const {
 }
 
 /* ************************************************************************* */
-boost::optional<Domain> Domain::checkAllDiff(const KeyVector keys,
+std::optional<Domain> Domain::checkAllDiff(const KeyVector keys,
                                              const Domains& domains) const {
   Key j = key();
   // for all values in this domain
@@ -74,7 +74,7 @@ boost::optional<Domain> Domain::checkAllDiff(const KeyVector keys,
     return Domain(this->discreteKey(), value);
   found:;
   }
-  return boost::none;  // we did not change it
+  return {};  // we did not change it
 }
 
 /* ************************************************************************* */
diff --git a/gtsam_unstable/discrete/Domain.h b/gtsam_unstable/discrete/Domain.h
index 1047101c5..5d96f0dc9 100644
--- a/gtsam_unstable/discrete/Domain.h
+++ b/gtsam_unstable/discrete/Domain.h
@@ -9,6 +9,7 @@
 
 #include <gtsam/discrete/DiscreteKey.h>
 #include <gtsam_unstable/discrete/Constraint.h>
+#include <optional>
 
 namespace gtsam {
 
@@ -100,7 +101,7 @@ class GTSAM_UNSTABLE_EXPORT Domain : public Constraint {
    * @param keys connected domains through alldiff
    * @param keys other domains
    */
-  boost::optional<Domain> checkAllDiff(const KeyVector keys,
+  std::optional<Domain> checkAllDiff(const KeyVector keys,
                                        const Domains& domains) const;
 
   /// Partially apply known values
diff --git a/gtsam_unstable/discrete/Scheduler.cpp b/gtsam_unstable/discrete/Scheduler.cpp
index b86df6c29..9543ab7cf 100644
--- a/gtsam_unstable/discrete/Scheduler.cpp
+++ b/gtsam_unstable/discrete/Scheduler.cpp
@@ -79,7 +79,7 @@ void Scheduler::addStudent(const string& studentName, const string& area1,
 
 /** get key for student and area, 0 is time slot itself */
 const DiscreteKey& Scheduler::key(size_t s,
-                                  boost::optional<size_t> area) const {
+                                  std::optional<size_t> area) const {
   return area ? students_[s].keys_[*area] : students_[s].key_;
 }
 
@@ -100,7 +100,7 @@ const string& Scheduler::studentArea(size_t i, size_t area) const {
 
 /** Add student-specific constraints to the graph */
 void Scheduler::addStudentSpecificConstraints(size_t i,
-                                              boost::optional<size_t> slot) {
+                                              std::optional<size_t> slot) {
   bool debug = ISDEBUG("Scheduler::buildGraph");
 
   assert(i < nrStudents());
diff --git a/gtsam_unstable/discrete/Scheduler.h b/gtsam_unstable/discrete/Scheduler.h
index 8d269e81a..f7b45d54a 100644
--- a/gtsam_unstable/discrete/Scheduler.h
+++ b/gtsam_unstable/discrete/Scheduler.h
@@ -108,7 +108,7 @@ class GTSAM_UNSTABLE_EXPORT Scheduler : public CSP {
 
   /** get key for student and area, 0 is time slot itself */
   const DiscreteKey& key(size_t s,
-                         boost::optional<size_t> area = boost::none) const;
+                         std::optional<size_t> area = {}) const;
 
   /** addStudent has to be called after adding slots and faculty */
   void addStudent(const std::string& studentName, const std::string& area1,
@@ -124,7 +124,7 @@ class GTSAM_UNSTABLE_EXPORT Scheduler : public CSP {
 
   /** Add student-specific constraints to the graph */
   void addStudentSpecificConstraints(
-      size_t i, boost::optional<size_t> slot = boost::none);
+      size_t i, std::optional<size_t> slot = {});
 
   /** Main routine that builds factor graph */
   void buildGraph(size_t mutexBound = 7);