diff --git a/csharp/src/Google.Protobuf/Reflection/FeatureSetDescriptor.g.cs b/csharp/src/Google.Protobuf/Reflection/FeatureSetDescriptor.g.cs
deleted file mode 100644
index 208ce1fcb6..0000000000
--- a/csharp/src/Google.Protobuf/Reflection/FeatureSetDescriptor.g.cs
+++ /dev/null
@@ -1,17 +0,0 @@
-#region Copyright notice and license
-// Protocol Buffers - Google's data interchange format
-// Copyright 2008 Google Inc.  All rights reserved.
-//
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file or at
-// https://developers.google.com/open-source/licenses/bsd
-#endregion
-
-namespace Google.Protobuf.Reflection;
-
-internal sealed partial class FeatureSetDescriptor
-{
-    // Canonical serialized form of the edition defaults, generated by embed_edition_defaults.
-    private const string DefaultsBase64 =
-        "ChMYhAciACoMCAEQAhgCIAMoATACChMY5wciACoMCAIQARgBIAIoATABChMY6AciDAgBEAEYASACKAEwASoAIOYHKOgH";
-}
diff --git a/hpb_generator/tests/child_model.proto b/hpb_generator/tests/child_model.proto
index 976a729725..ba410d25f5 100644
--- a/hpb_generator/tests/child_model.proto
+++ b/hpb_generator/tests/child_model.proto
@@ -5,22 +5,25 @@
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
-syntax = "proto3";
+edition = "2023";
 
 package hpb_unittest;
 
 import public "google/protobuf/compiler/hpb/tests/test_enum.proto";
 
 message ChildModel1 {
-  optional bool child_b1 = 44;
-  optional string child_str1 = 56;
+  bool child_b1 = 44;
+  string child_str1 = 56;
 }
 
 message ChildModel3 {
-  string sub_key = 1;
-  bool bool1 = 2;
-  int32 i32 = 3;
-  optional string opt_str = 4;
-  optional bool opt_bool = 5;
-  optional int32 opt_i32 = 6;
+  string sub_key = 1 [features.field_presence = IMPLICIT];
+
+  bool bool1 = 2 [features.field_presence = IMPLICIT];
+
+  int32 i32 = 3 [features.field_presence = IMPLICIT];
+
+  string opt_str = 4;
+  bool opt_bool = 5;
+  int32 opt_i32 = 6;
 }
diff --git a/hpb_generator/tests/legacy-name.proto b/hpb_generator/tests/legacy-name.proto
index dbe1b8f751..d16d0adb3b 100644
--- a/hpb_generator/tests/legacy-name.proto
+++ b/hpb_generator/tests/legacy-name.proto
@@ -5,7 +5,7 @@
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
-syntax = "proto3";
+edition = "2023";
 
 package hpb_unittest;
 
diff --git a/hpb_generator/tests/naming_conflict.proto b/hpb_generator/tests/naming_conflict.proto
index 917d4e0d29..2b456937c1 100644
--- a/hpb_generator/tests/naming_conflict.proto
+++ b/hpb_generator/tests/naming_conflict.proto
@@ -5,11 +5,11 @@
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
-syntax = "proto3";
+edition = "2023";
 
 package hpb_unittest;
 
 message HasChildCount {
-  optional HasChildCount has_child_count = 1;
-  optional int32 child_count = 2;
+  HasChildCount has_child_count = 1;
+  int32 child_count = 2;
 }
diff --git a/hpb_generator/tests/no_package.proto b/hpb_generator/tests/no_package.proto
index ebd9c2fda6..799ff3841d 100644
--- a/hpb_generator/tests/no_package.proto
+++ b/hpb_generator/tests/no_package.proto
@@ -5,8 +5,9 @@
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
-syntax = "proto2";
+edition = "2023";
 
+option features.enum_type = CLOSED;
 // option java_multiple_files = true;
 
 enum EnumWithNoPackage {
diff --git a/hpb_generator/tests/no_package_enum_user.proto b/hpb_generator/tests/no_package_enum_user.proto
index 703fa2ab44..21cda76bfa 100644
--- a/hpb_generator/tests/no_package_enum_user.proto
+++ b/hpb_generator/tests/no_package_enum_user.proto
@@ -5,7 +5,7 @@
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
-syntax = "proto2";
+edition = "2023";
 
 package hpb_unittest;
 
@@ -14,5 +14,5 @@ import "google/protobuf/compiler/hpb/tests/no_package.proto";
 // option java_multiple_files = true;
 
 message MyMessage {
-  optional MessageWithEnumUpbTest my_type = 1;
+  MessageWithEnumUpbTest my_type = 1;
 }
diff --git a/hpb_generator/tests/set_alias.proto b/hpb_generator/tests/set_alias.proto
index b279c0c6b4..a8566e7bc1 100644
--- a/hpb_generator/tests/set_alias.proto
+++ b/hpb_generator/tests/set_alias.proto
@@ -5,18 +5,18 @@
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
-syntax = "proto2";
+edition = "2023";
 
 package hpb_unittest;
 
 message Child {
-  optional int32 peeps = 1;
+  int32 peeps = 1;
 }
 
 message Parent {
-  optional int32 x = 2;
-  optional Child child = 3;
-  optional int64 out_of_order = 1;  // set_alias must work regardless of order
+  int32 x = 2;
+  Child child = 3;
+  int64 out_of_order = 1;  // set_alias must work regardless of order
 }
 
 message ParentWithRepeated {
diff --git a/hpb_generator/tests/test_enum.proto b/hpb_generator/tests/test_enum.proto
index 7f76cce495..03afd87f27 100644
--- a/hpb_generator/tests/test_enum.proto
+++ b/hpb_generator/tests/test_enum.proto
@@ -5,7 +5,7 @@
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
-syntax = "proto3";
+edition = "2023";
 
 package hpb_unittest;
 
diff --git a/hpb_generator/tests/test_extension.proto b/hpb_generator/tests/test_extension.proto
index e8ff9d5329..c2578efdec 100644
--- a/hpb_generator/tests/test_extension.proto
+++ b/hpb_generator/tests/test_extension.proto
@@ -5,7 +5,7 @@
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
-syntax = "proto2";
+edition = "2023";
 
 package hpb_unittest.someotherpackage;
 
@@ -15,10 +15,11 @@ import "google/protobuf/compiler/hpb/tests/test_model.proto";
 // defined in different file.
 
 extend TestModel {
-  optional ThemeExtension styling = 13001;
+  ThemeExtension styling = 13001;
 }
 
 extend TestModel {
-  optional int32 int32_ext = 13002 [default = 644];
-  optional int64 int64_ext = 13003 [default = 2147483648];
+  int32 int32_ext = 13002 [default = 644];
+
+  int64 int64_ext = 13003 [default = 2147483648];
 }
diff --git a/hpb_generator/tests/test_model.proto b/hpb_generator/tests/test_model.proto
index 8a5401b6b7..5bb50be1a2 100644
--- a/hpb_generator/tests/test_model.proto
+++ b/hpb_generator/tests/test_model.proto
@@ -5,74 +5,89 @@
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
-syntax = "proto2";
+edition = "2023";
 
 package hpb_unittest;
 
 import "google/protobuf/compiler/hpb/tests/child_model.proto";
+import "google/protobuf/cpp_features.proto";
+
+option features.enum_type = CLOSED;
+option features.repeated_field_encoding = EXPANDED;
+option features.utf8_validation = NONE;
 
 message TestModelContainer {
   repeated TestModel models = 1;
-  optional ChildModel3 proto_3_child = 2;
+  ChildModel3 proto_3_child = 2;
+
   extensions 10000 to max
   [verification = UNVERIFIED];
 }
 
 message TestModel {
-  optional int32 value = 1;
+  int32 value = 1;
   repeated int32 value_array = 2;  // _UPB_MODE_ARRAY
   repeated int32 value_packed_array = 3
-      [packed = true];  // _UPB_MODE_ARRAY | _UPB_MODE_IS_PACKED
+      [features.repeated_field_encoding =
+           PACKED];  // _UPB_MODE_ARRAY | _UPB_MODE_IS_PACKED
+
   repeated int32 value_deprec = 4 [deprecated = true];
-  optional string str1 = 115;
-  optional bool b1 = 9;
-  optional bool b2 = 10;
-  optional string str2 = 50;
-  optional string str3 = 11;
-  optional float optional_float = 14;
-  optional double optional_double = 15;
-  optional int64 optional_int64 = 16;
-  optional uint32 optional_uint32 = 17;
-  optional uint64 optional_uint64 = 18;
-  optional sint32 optional_sint32 = 19;
-  optional sint64 optional_sint64 = 20;
-  optional fixed32 optional_fixed32 = 21;
-  optional fixed64 optional_fixed64 = 22;
-  optional sfixed32 optional_sfixed32 = 23;
-  optional sfixed64 optional_sfixed64 = 24;
+
+  string str1 = 115;
+  bool b1 = 9;
+  bool b2 = 10;
+  string str2 = 50;
+  string str3 = 11;
+  float optional_float = 14;
+  double optional_double = 15;
+  int64 optional_int64 = 16;
+  uint32 optional_uint32 = 17;
+  uint64 optional_uint64 = 18;
+  sint32 optional_sint32 = 19;
+  sint64 optional_sint64 = 20;
+  fixed32 optional_fixed32 = 21;
+  fixed64 optional_fixed64 = 22;
+  sfixed32 optional_sfixed32 = 23;
+  sfixed64 optional_sfixed64 = 24;
   repeated int64 repeated_int64 = 25;
   repeated uint64 repeated_uint64 = 26;
   repeated fixed64 repeated_fixed64 = 27;
   repeated sfixed64 repeated_sfixed64 = 28;
   repeated bool repeated_bool = 29;
   repeated string repeated_string = 35;
-  optional bytes optional_bytes = 36;
+  bytes optional_bytes = 36;
+
   message NestedChild {
-    optional string nested_child_name = 211;
+    string nested_child_name = 211;
   }
-  optional NestedChild nested_child_1 = 212;
-  optional ChildModel1 child_model_1 = 222;
+
+  NestedChild nested_child_1 = 212;
+  ChildModel1 child_model_1 = 222;
   repeated ChildModel1 child_models = 223;
-  optional ChildModel1 bar = 224;
+  ChildModel1 bar = 224;
+
   oneof child_oneof1 {
     string oneof_member1 = 98;
     bool oneof_member2 = 99;
   }
-  optional int32 int_value_with_default = 31
-      [default = 65];  // Not supported yet
-  optional string string_value_with_default = 32
+
+  int32 int_value_with_default = 31 [default = 65];  // Not supported yet
+
+  string string_value_with_default = 32
       [default = "hello"];  // Not supported yet
-  optional float float_value_with_default = 33 [default = inf];
-  optional float double_value_with_default = 34 [default = -inf];
+
+  float float_value_with_default = 33 [default = inf];
+
+  float double_value_with_default = 34 [default = -inf];
 
   map<int32, ChildModel1> child_map = 225;
-  optional TestModel recursive_child = 226;
+  TestModel recursive_child = 226;
   map<string, ChildModel1> child_str_map = 227;
   map<string, int32> str_to_int_map = 228;
   map<string, string> str_to_str_map = 229;
 
   extend TestAnnotation {
-    optional OtherExtension in_message_ext = 15000;
+    OtherExtension in_message_ext = 15000;
   }
 
   enum Category {
@@ -81,7 +96,8 @@ message TestModel {
     VIDEO = 7;
     RADIO = 8 [deprecated = true];
   }
-  optional Category category = 37;
+
+  Category category = 37;
 
   // keyword collisions (double, template, ...)
   oneof type {
@@ -89,18 +105,18 @@ message TestModel {
     int64 int64 = 231;
     double double = 232;
   }
-  optional string template = 233;
-  optional string msg = 234;
-  optional string arena = 235;
 
-  // Tests publicly imported enum.
-  optional TestEnum imported_enum = 238;
+  string template = 233;
+  string msg = 234;
+  string arena = 235;
 
-  optional string phase = 239;
-  optional bool clear_phase = 240;
+  // Tests publicly imported enum.
+  TestEnum imported_enum = 238;
 
-  optional string doc_id = 241;
-  optional bool set_doc_id = 242;
+  string phase = 239;
+  bool clear_phase = 240;
+  string doc_id = 241;
+  bool set_doc_id = 242;
 
   extensions 10000 to max
   [verification = UNVERIFIED];
@@ -112,13 +128,15 @@ message TestModelContainerV1 {
 }
 
 message TestModelV1 {
-  optional int32 value = 1;
+  int32 value = 1;
   repeated int32 value2 = 2;
-  repeated int32 value3 = 3 [packed = true];
+  repeated int32 value3 = 3 [features.repeated_field_encoding = PACKED];
+
   repeated int32 value4 = 4 [deprecated = true];
-  optional bool b1 = 9;
-  optional bool b2 = 10;
-  optional string str2 = 50;
+
+  bool b1 = 9;
+  bool b2 = 10;
+  string str2 = 50;
 }
 
 enum PrimaryColors {
@@ -130,33 +148,35 @@ enum PrimaryColors {
 // TestModel extension.
 message ThemeExtension {
   extend TestModel {
-    optional ThemeExtension theme_extension = 12003;
+    ThemeExtension theme_extension = 12003;
   }
-  optional string ext_name = 1;
-  optional bool ext_bool = 2;
+
+  string ext_name = 1;
+  bool ext_bool = 2;
 }
 
 extend TestModel {
-  optional ThemeExtension theme = 12001;
+  ThemeExtension theme = 12001;
 }
 
 message ContainerExtension {
   extend TestModelContainer {
-    optional ContainerExtension container_extension = 12004;
+    ContainerExtension container_extension = 12004;
   }
-  optional string ext_container_name = 1;
+
+  string ext_container_name = 1;
 }
 
 extend TestModelContainer {
-  optional ContainerExtension container_ext = 12005;
+  ContainerExtension container_ext = 12005;
 }
 
 message OtherExtension {
-  optional string ext2_name = 1;
+  string ext2_name = 1;
 }
 
 extend TestModel {
-  optional OtherExtension other_ext = 12002;
+  OtherExtension other_ext = 12002;
 }
 
 message TestAnnotation {
@@ -165,7 +185,7 @@ message TestAnnotation {
 }
 
 message TestMessageHasEnum {
-  optional EnumDeclaredAfterMessage enum_declared_after_message = 1;
+  EnumDeclaredAfterMessage enum_declared_after_message = 1;
 }
 
 enum EnumDeclaredAfterMessage {