diff --git a/eval/public/structs/cel_proto_wrap_util.cc b/eval/public/structs/cel_proto_wrap_util.cc
index d0f80171f..7bfe81fe6 100644
--- a/eval/public/structs/cel_proto_wrap_util.cc
+++ b/eval/public/structs/cel_proto_wrap_util.cc
@@ -691,7 +691,7 @@ class ValueFromMessageMaker {
         return CreateWellknownTypeValue<Struct>(message, factory, arena);
       // WELLKNOWNTYPE_FIELDMASK has no special CelValue type
       default:
-        return absl::nullopt;
+        return std::nullopt;
     }
   }
 
@@ -716,7 +716,7 @@ absl::optional<CelValue> DynamicMap::operator[](CelValue key) const {
 
   auto it = values_->fields().find(std::string(str_key.value()));
   if (it == values_->fields().end()) {
-    return absl::nullopt;
+    return std::nullopt;
   }
 
   return ValueManager(factory_, arena_).ValueFromMessage(&it->second);
diff --git a/eval/public/structs/cel_proto_wrapper.cc b/eval/public/structs/cel_proto_wrapper.cc
index a1dc83ade..6fad6aee3 100644
--- a/eval/public/structs/cel_proto_wrapper.cc
+++ b/eval/public/structs/cel_proto_wrapper.cc
@@ -53,7 +53,7 @@ absl::optional<CelValue> CelProtoWrapper::MaybeWrapValue(
   if (msg != nullptr) {
     return InternalWrapMessage(msg);
   } else {
-    return absl::nullopt;
+    return std::nullopt;
   }
 }
 
diff --git a/eval/public/structs/legacy_type_provider.cc b/eval/public/structs/legacy_type_provider.cc
index f87ab9645..f8db92298 100644
--- a/eval/public/structs/legacy_type_provider.cc
+++ b/eval/public/structs/legacy_type_provider.cc
@@ -63,7 +63,7 @@ class LegacyStructValueBuilder final : public cel::StructValueBuilder {
     CEL_RETURN_IF_ERROR(adapter_.mutation_apis()->SetField(
                             name, legacy_value, memory_manager_, builder_))
         .With(cel::ErrorValueReturn());
-    return absl::nullopt;
+    return std::nullopt;
   }
 
   absl::StatusOr<absl::optional<cel::ErrorValue>> SetFieldByNumber(
@@ -76,7 +76,7 @@ class LegacyStructValueBuilder final : public cel::StructValueBuilder {
     CEL_RETURN_IF_ERROR(adapter_.mutation_apis()->SetFieldByNumber(
                             number, legacy_value, memory_manager_, builder_))
         .With(cel::ErrorValueReturn());
-    return absl::nullopt;
+    return std::nullopt;
   }
 
   absl::StatusOr<cel::StructValue> Build() && override {
@@ -116,7 +116,7 @@ class LegacyValueBuilder final : public cel::ValueBuilder {
     CEL_RETURN_IF_ERROR(adapter_.mutation_apis()->SetField(
                             name, legacy_value, memory_manager_, builder_))
         .With(cel::ErrorValueReturn());
-    return absl::nullopt;
+    return std::nullopt;
   }
 
   absl::StatusOr<absl::optional<cel::ErrorValue>> SetFieldByNumber(
@@ -129,7 +129,7 @@ class LegacyValueBuilder final : public cel::ValueBuilder {
     CEL_RETURN_IF_ERROR(adapter_.mutation_apis()->SetFieldByNumber(
                             number, legacy_value, memory_manager_, builder_))
         .With(cel::ErrorValueReturn());
-    return absl::nullopt;
+    return std::nullopt;
   }
 
   absl::StatusOr<cel::Value> Build() && override {
@@ -187,7 +187,7 @@ absl::StatusOr<absl::optional<cel::Type>> LegacyTypeProvider::FindTypeImpl(
     return cel::common_internal::MakeBasicStructType(
         (*type_info)->GetTypename(MessageWrapper()));
   }
-  return absl::nullopt;
+  return std::nullopt;
 }
 
 absl::StatusOr<absl::optional<cel::StructTypeField>>
@@ -206,13 +206,13 @@ LegacyTypeProvider::FindStructTypeFieldByNameImpl(
       const auto* mutation_apis =
           (*type_info)->GetMutationApis(MessageWrapper());
       if (mutation_apis == nullptr || !mutation_apis->DefinesField(name)) {
-        return absl::nullopt;
+        return std::nullopt;
       }
       return cel::common_internal::BasicStructTypeField(name, 0,
                                                         cel::DynType{});
     }
   }
-  return absl::nullopt;
+  return std::nullopt;
 }
 
 }  // namespace google::api::expr::runtime
diff --git a/eval/public/structs/legacy_type_provider_test.cc b/eval/public/structs/legacy_type_provider_test.cc
index 160ac49f3..8de2aba01 100644
--- a/eval/public/structs/legacy_type_provider_test.cc
+++ b/eval/public/structs/legacy_type_provider_test.cc
@@ -28,7 +28,7 @@ class LegacyTypeProviderTestEmpty : public LegacyTypeProvider {
  public:
   absl::optional<LegacyTypeAdapter> ProvideLegacyType(
       absl::string_view name) const override {
-    return absl::nullopt;
+    return std::nullopt;
   }
 };
 
@@ -60,14 +60,14 @@ class LegacyTypeProviderTestImpl : public LegacyTypeProvider {
     if (name == "test") {
       return LegacyTypeAdapter(nullptr, nullptr);
     }
-    return absl::nullopt;
+    return std::nullopt;
   }
   absl::optional<const LegacyTypeInfoApis*> ProvideLegacyTypeInfo(
       absl::string_view name) const override {
     if (name == "test") {
       return test_type_info_;
     }
-    return absl::nullopt;
+    return std::nullopt;
   }
 
  private:
@@ -76,8 +76,8 @@ class LegacyTypeProviderTestImpl : public LegacyTypeProvider {
 
 TEST(LegacyTypeProviderTest, EmptyTypeProviderHasProvideTypeInfo) {
   LegacyTypeProviderTestEmpty provider;
-  EXPECT_EQ(provider.ProvideLegacyType("test"), absl::nullopt);
-  EXPECT_EQ(provider.ProvideLegacyTypeInfo("test"), absl::nullopt);
+  EXPECT_EQ(provider.ProvideLegacyType("test"), std::nullopt);
+  EXPECT_EQ(provider.ProvideLegacyTypeInfo("test"), std::nullopt);
 }
 
 TEST(LegacyTypeProviderTest, NonEmptyTypeProviderProvidesSomeTypes) {
@@ -85,8 +85,8 @@ TEST(LegacyTypeProviderTest, NonEmptyTypeProviderProvidesSomeTypes) {
   LegacyTypeProviderTestImpl provider(&test_type_info);
   EXPECT_TRUE(provider.ProvideLegacyType("test").has_value());
   EXPECT_TRUE(provider.ProvideLegacyTypeInfo("test").has_value());
-  EXPECT_EQ(provider.ProvideLegacyType("other"), absl::nullopt);
-  EXPECT_EQ(provider.ProvideLegacyTypeInfo("other"), absl::nullopt);
+  EXPECT_EQ(provider.ProvideLegacyType("other"), std::nullopt);
+  EXPECT_EQ(provider.ProvideLegacyTypeInfo("other"), std::nullopt);
 }
 
 }  // namespace
diff --git a/eval/public/structs/proto_message_type_adapter.cc b/eval/public/structs/proto_message_type_adapter.cc
index 6a3417ba3..8c140c0c7 100644
--- a/eval/public/structs/proto_message_type_adapter.cc
+++ b/eval/public/structs/proto_message_type_adapter.cc
@@ -472,14 +472,14 @@ const LegacyTypeAccessApis* ProtoMessageTypeAdapter::GetAccessApis(
 absl::optional<LegacyTypeInfoApis::FieldDescription>
 ProtoMessageTypeAdapter::FindFieldByName(absl::string_view field_name) const {
   if (descriptor_ == nullptr) {
-    return absl::nullopt;
+    return std::nullopt;
   }
 
   const google::protobuf::FieldDescriptor* field_descriptor =
       descriptor_->FindFieldByName(field_name);
 
   if (field_descriptor == nullptr) {
-    return absl::nullopt;
+    return std::nullopt;
   }
 
   return LegacyTypeInfoApis::FieldDescription{field_descriptor->number(),
diff --git a/eval/public/structs/proto_message_type_adapter_test.cc b/eval/public/structs/proto_message_type_adapter_test.cc
index 32608bc3f..8f295aff8 100644
--- a/eval/public/structs/proto_message_type_adapter_test.cc
+++ b/eval/public/structs/proto_message_type_adapter_test.cc
@@ -709,7 +709,7 @@ TEST(ProtoMesssageTypeAdapter, FindFieldNotFound) {
           "google.api.expr.runtime.TestMessage"),
       google::protobuf::MessageFactory::generated_factory());
 
-  EXPECT_EQ(adapter.FindFieldByName("foo_not_a_field"), absl::nullopt);
+  EXPECT_EQ(adapter.FindFieldByName("foo_not_a_field"), std::nullopt);
 }
 
 TEST(ProtoMesssageTypeAdapter, TypeInfoMutator) {
diff --git a/eval/public/structs/protobuf_descriptor_type_provider.cc b/eval/public/structs/protobuf_descriptor_type_provider.cc
index 68b39c643..b5746523e 100644
--- a/eval/public/structs/protobuf_descriptor_type_provider.cc
+++ b/eval/public/structs/protobuf_descriptor_type_provider.cc
@@ -27,7 +27,7 @@ absl::optional<LegacyTypeAdapter> ProtobufDescriptorProvider::ProvideLegacyType(
     absl::string_view name) const {
   const ProtoMessageTypeAdapter* result = GetTypeAdapter(name);
   if (result == nullptr) {
-    return absl::nullopt;
+    return std::nullopt;
   }
   // ProtoMessageTypeAdapter provides apis for both access and mutation.
   return LegacyTypeAdapter(result, result);
@@ -38,7 +38,7 @@ ProtobufDescriptorProvider::ProvideLegacyTypeInfo(
     absl::string_view name) const {
   const ProtoMessageTypeAdapter* result = GetTypeAdapter(name);
   if (result == nullptr) {
-    return absl::nullopt;
+    return std::nullopt;
   }
   return result;
 }
diff --git a/eval/public/structs/trivial_legacy_type_info_test.cc b/eval/public/structs/trivial_legacy_type_info_test.cc
index 9b4840373..9cc6e4916 100644
--- a/eval/public/structs/trivial_legacy_type_info_test.cc
+++ b/eval/public/structs/trivial_legacy_type_info_test.cc
@@ -56,9 +56,9 @@ TEST(TrivialTypeInfo, FindFieldByName) {
   TrivialTypeInfo info;
   MessageWrapper wrapper;
 
-  EXPECT_EQ(info.FindFieldByName("foo"), absl::nullopt);
+  EXPECT_EQ(info.FindFieldByName("foo"), std::nullopt);
   EXPECT_EQ(TrivialTypeInfo::GetInstance()->FindFieldByName("foo"),
-            absl::nullopt);
+            std::nullopt);
 }
 
 }  // namespace