diff --git a/protobuf/CHANGELOG.md b/protobuf/CHANGELOG.md
index 6b2d55b6..7cf13e1f 100644
--- a/protobuf/CHANGELOG.md
+++ b/protobuf/CHANGELOG.md
@@ -1,3 +1,5 @@
+## 5.0.0-wip
+
 ## 4.2.0
 
 * Internal refactoring to split the package into libraries. This allows
@@ -11,6 +13,9 @@
 * Improve performance of `GeneratedMessage` members: `writeToJsonMap`,
   `writeToJson`, `mergeFromJson`, `mergeFromJsonMap`. ([#1028])
 
+* Remove `BuilderInfo.fromProto3Json` and `BuilderInfo.toProto3Json` as a part
+  of an internal refactoring.
+
 [#1026]: https://github.com/google/protobuf.dart/pull/1026
 [#1027]: https://github.com/google/protobuf.dart/pull/1027
 [#1028]: https://github.com/google/protobuf.dart/pull/1028
diff --git a/protobuf/lib/protobuf.dart b/protobuf/lib/protobuf.dart
index d1e569bd..67bfad99 100644
--- a/protobuf/lib/protobuf.dart
+++ b/protobuf/lib/protobuf.dart
@@ -18,4 +18,6 @@ export 'src/protobuf/internal.dart'
         GeneratedMessageInternalExtension,
         MapFieldInfoInternalExtension,
         mapKeyFieldNumber,
-        mapValueFieldNumber;
+        mapValueFieldNumber,
+        mergeFromProto3JsonAny,
+        writeToProto3JsonAny;
diff --git a/protobuf/lib/src/protobuf/builder_info.dart b/protobuf/lib/src/protobuf/builder_info.dart
index d21b3dfa..d98858f3 100644
--- a/protobuf/lib/src/protobuf/builder_info.dart
+++ b/protobuf/lib/src/protobuf/builder_info.dart
@@ -42,24 +42,17 @@ class BuilderInfo {
   List<FieldInfo>? _sortedByTag;
 
   // For well-known types.
-  final Object? Function(GeneratedMessage message, TypeRegistry typeRegistry)?
-  toProto3Json;
-  final Function(
-    GeneratedMessage targetMessage,
-    Object json,
-    TypeRegistry typeRegistry,
-    JsonParsingContext context,
-  )?
-  fromProto3Json;
+  final WellKnownType? _wellKnownType;
+
   final CreateBuilderFunc? createEmptyInstance;
 
   BuilderInfo(
     String? messageName, {
     PackageName package = const PackageName(''),
     this.createEmptyInstance,
-    this.toProto3Json,
-    this.fromProto3Json,
-  }) : qualifiedMessageName = '${package.prefix}$messageName';
+    WellKnownType? wellKnownType,
+  }) : qualifiedMessageName = '${package.prefix}$messageName',
+       _wellKnownType = wellKnownType;
 
   void add<T>(
     int tagNumber,
diff --git a/protobuf/lib/src/protobuf/internal.dart b/protobuf/lib/src/protobuf/internal.dart
index e3a29d07..95d491ef 100644
--- a/protobuf/lib/src/protobuf/internal.dart
+++ b/protobuf/lib/src/protobuf/internal.dart
@@ -18,6 +18,7 @@ import 'package:meta/meta.dart' show UseResult;
 import 'consts.dart';
 import 'json/json.dart' as json_lib;
 import 'json_parsing_context.dart';
+import 'mixins/well_known.dart';
 import 'permissive_compare.dart';
 import 'type_registry.dart';
 import 'utils.dart';
diff --git a/protobuf/lib/src/protobuf/mixins/well_known.dart b/protobuf/lib/src/protobuf/mixins/well_known.dart
index 644d92a0..bf63a434 100644
--- a/protobuf/lib/src/protobuf/mixins/well_known.dart
+++ b/protobuf/lib/src/protobuf/mixins/well_known.dart
@@ -6,9 +6,30 @@ import 'dart:convert';
 
 import 'package:fixnum/fixnum.dart';
 
-import '../../../protobuf.dart';
+import '../internal.dart';
 import '../json_parsing_context.dart';
 
+/// The set of well known protobuf message types which may have customized
+/// serialization logic.
+enum WellKnownType {
+  any,
+  timestamp,
+  duration,
+  struct,
+  value,
+  listValue,
+  fieldMask,
+  doubleValue,
+  floatValue,
+  int64Value,
+  uint64Value,
+  int32Value,
+  uint32Value,
+  boolValue,
+  stringValue,
+  bytesValue,
+}
+
 mixin AnyMixin implements GeneratedMessage {
   String get typeUrl;
   set typeUrl(String value);
@@ -98,14 +119,7 @@ mixin AnyMixin implements GeneratedMessage {
       );
     }
     final unpacked = info.createEmptyInstance!()..mergeFromBuffer(any.value);
-    final proto3Json = unpacked.toProto3Json(typeRegistry: typeRegistry);
-    if (info.toProto3Json == null) {
-      final map = proto3Json as Map<String, dynamic>;
-      map['@type'] = any.typeUrl;
-      return map;
-    } else {
-      return {'@type': any.typeUrl, 'value': proto3Json};
-    }
+    return writeToProto3JsonAny(unpacked.fieldSet, any.typeUrl, typeRegistry);
   }
 
   static void fromProto3JsonHelper(
@@ -133,21 +147,13 @@ mixin AnyMixin implements GeneratedMessage {
         );
       }
 
-      final Object? subJson =
-          info.fromProto3Json == null
-              // TODO(sigurdm): avoid cloning [object] here.
-              ? (Map<String, dynamic>.from(object)..remove('@type'))
-              : object['value'];
-      // TODO(sigurdm): We lose [context.path].
-      final packedMessage =
-          info.createEmptyInstance!()..mergeFromProto3Json(
-            subJson,
-            typeRegistry: typeRegistry,
-            supportNamesWithUnderscores: context.supportNamesWithUnderscores,
-            ignoreUnknownFields: context.ignoreUnknownFields,
-            permissiveEnums: context.permissiveEnums,
-          );
-
+      final packedMessage = info.createEmptyInstance!();
+      mergeFromProto3JsonAny(
+        json,
+        packedMessage.fieldSet,
+        typeRegistry,
+        context,
+      );
       any.value = packedMessage.writeToBuffer();
       any.typeUrl = typeUrl;
     } else {
diff --git a/protobuf/lib/src/protobuf/proto3_json.dart b/protobuf/lib/src/protobuf/proto3_json.dart
index 0fe4849c..de0c2428 100644
--- a/protobuf/lib/src/protobuf/proto3_json.dart
+++ b/protobuf/lib/src/protobuf/proto3_json.dart
@@ -4,6 +4,40 @@
 
 part of 'internal.dart';
 
+// Public because this is called from the mixins library.
+Object writeToProto3JsonAny(
+  FieldSet fs,
+  String typeUrl,
+  TypeRegistry typeRegistry,
+) {
+  final result = _writeToProto3Json(fs, typeRegistry);
+  final wellKnownType = fs._meta._wellKnownType;
+  if (wellKnownType != null) {
+    switch (wellKnownType) {
+      case WellKnownType.any:
+      case WellKnownType.timestamp:
+      case WellKnownType.duration:
+      case WellKnownType.struct:
+      case WellKnownType.value:
+      case WellKnownType.listValue:
+      case WellKnownType.fieldMask:
+      case WellKnownType.doubleValue:
+      case WellKnownType.floatValue:
+      case WellKnownType.int64Value:
+      case WellKnownType.uint64Value:
+      case WellKnownType.int32Value:
+      case WellKnownType.uint32Value:
+      case WellKnownType.boolValue:
+      case WellKnownType.stringValue:
+      case WellKnownType.bytesValue:
+        return {'@type': typeUrl, 'value': result};
+    }
+  }
+
+  (result as Map<String, dynamic>)['@type'] = typeUrl;
+  return result;
+}
+
 Object? _writeToProto3Json(FieldSet fs, TypeRegistry typeRegistry) {
   String? convertToMapKey(dynamic key, int keyType) {
     final baseType = PbFieldType.baseType(keyType);
@@ -86,8 +120,46 @@ Object? _writeToProto3Json(FieldSet fs, TypeRegistry typeRegistry) {
   }
 
   final meta = fs._meta;
-  if (meta.toProto3Json != null) {
-    return meta.toProto3Json!(fs._message!, typeRegistry);
+  final wellKnownType = meta._wellKnownType;
+  if (wellKnownType != null) {
+    switch (wellKnownType) {
+      case WellKnownType.any:
+        return AnyMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.timestamp:
+        return TimestampMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.duration:
+        return DurationMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.struct:
+        return StructMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.value:
+        return ValueMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.listValue:
+        return ListValueMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.fieldMask:
+        return FieldMaskMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.doubleValue:
+        return DoubleValueMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.floatValue:
+        return FloatValueMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.int64Value:
+        return Int64ValueMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.uint64Value:
+        return UInt64ValueMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.int32Value:
+        return Int32ValueMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.uint32Value:
+        return UInt32ValueMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.boolValue:
+        return BoolValueMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.stringValue:
+        return StringValueMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+      case WellKnownType.bytesValue:
+        return BytesValueMixin.toProto3JsonHelper(fs._message!, typeRegistry);
+    }
+    // [WellKnownType] could be used to for messages which have special
+    // encodings in other codecs. The set of messages which special encodings in
+    // proto3json is handled here, so we intentionally fall through to the
+    // default message handling rather than throwing.
   }
 
   final result = <String, dynamic>{};
@@ -156,6 +228,56 @@ extension _FindFirst<E> on Iterable<E> {
   }
 }
 
+// Public because this is called from the mixins library.
+void mergeFromProto3JsonAny(
+  Object? json,
+  FieldSet fieldSet,
+  TypeRegistry typeRegistry,
+  JsonParsingContext context,
+) {
+  if (json is! Map<String, dynamic>) {
+    throw context.parseException('Expected JSON object', json);
+  }
+
+  final wellKnownType = fieldSet._meta._wellKnownType;
+  if (wellKnownType != null) {
+    switch (wellKnownType) {
+      case WellKnownType.any:
+      case WellKnownType.timestamp:
+      case WellKnownType.duration:
+      case WellKnownType.struct:
+      case WellKnownType.value:
+      case WellKnownType.listValue:
+      case WellKnownType.fieldMask:
+      case WellKnownType.doubleValue:
+      case WellKnownType.floatValue:
+      case WellKnownType.int64Value:
+      case WellKnownType.uint64Value:
+      case WellKnownType.int32Value:
+      case WellKnownType.uint32Value:
+      case WellKnownType.boolValue:
+      case WellKnownType.stringValue:
+      case WellKnownType.bytesValue:
+        final value = json['value'];
+        return _mergeFromProto3JsonWithContext(
+          value,
+          fieldSet,
+          typeRegistry,
+          context,
+        );
+    }
+  }
+
+  // TODO(sigurdm): avoid cloning [object] here.
+  final withoutType = Map<String, dynamic>.from(json)..remove('@type');
+  return _mergeFromProto3JsonWithContext(
+    withoutType,
+    fieldSet,
+    typeRegistry,
+    context,
+  );
+}
+
 /// Merge a JSON object representing a message in proto3 JSON format ([json])
 /// to [fieldSet].
 void _mergeFromProto3Json(
@@ -166,12 +288,23 @@ void _mergeFromProto3Json(
   bool supportNamesWithUnderscores,
   bool permissiveEnums,
 ) {
-  fieldSet._ensureWritable();
   final context = JsonParsingContext(
     ignoreUnknownFields,
     supportNamesWithUnderscores,
     permissiveEnums,
   );
+  return _mergeFromProto3JsonWithContext(json, fieldSet, typeRegistry, context);
+}
+
+/// Merge a JSON object representing a message in proto3 JSON format ([json])
+/// to [fieldSet].
+void _mergeFromProto3JsonWithContext(
+  Object? json,
+  FieldSet fieldSet,
+  TypeRegistry typeRegistry,
+  JsonParsingContext context,
+) {
+  fieldSet._ensureWritable();
 
   void recursionHelper(Object? json, FieldSet fieldSet) {
     Object? convertProto3JsonValue(Object value, FieldInfo fieldInfo) {
@@ -225,16 +358,16 @@ void _mergeFromProto3Json(
           if (value is String) {
             // TODO(sigurdm): Do we want to avoid linear search here? Measure...
             final result =
-                permissiveEnums
+                context.permissiveEnums
                     ? fieldInfo.enumValues!.findFirst(
                       (e) => permissiveCompare(e.name, value),
                     )
                     : fieldInfo.enumValues!.findFirst((e) => e.name == value);
-            if ((result != null) || ignoreUnknownFields) return result;
+            if ((result != null) || context.ignoreUnknownFields) return result;
             throw context.parseException('Unknown enum value', value);
           } else if (value is int) {
             return fieldInfo.valueOf!(value) ??
-                (ignoreUnknownFields
+                (context.ignoreUnknownFields
                     ? null
                     : (throw context.parseException(
                       'Unknown enum value',
@@ -368,99 +501,227 @@ void _mergeFromProto3Json(
     }
 
     final meta = fieldSet._meta;
-    final wellKnownConverter = meta.fromProto3Json;
-    if (wellKnownConverter != null) {
-      wellKnownConverter(fieldSet._message!, json, typeRegistry, context);
-    } else {
-      if (json is Map) {
-        final byName = meta.byName;
+    final wellKnownType = meta._wellKnownType;
+    if (wellKnownType != null) {
+      switch (wellKnownType) {
+        case WellKnownType.any:
+          AnyMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.timestamp:
+          TimestampMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.duration:
+          DurationMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.struct:
+          StructMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.value:
+          ValueMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.listValue:
+          ListValueMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.fieldMask:
+          FieldMaskMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.doubleValue:
+          DoubleValueMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.floatValue:
+          FloatValueMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.int64Value:
+          Int64ValueMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.uint64Value:
+          UInt64ValueMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.int32Value:
+          Int32ValueMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.uint32Value:
+          UInt32ValueMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.boolValue:
+          BoolValueMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.stringValue:
+          StringValueMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+        case WellKnownType.bytesValue:
+          BytesValueMixin.fromProto3JsonHelper(
+            fieldSet._message!,
+            json,
+            typeRegistry,
+            context,
+          );
+          return;
+      }
 
-        json.forEach((key, Object? value) {
-          if (value == null) {
-            return;
-          }
-          if (key is! String) {
-            throw context.parseException('Key was not a String', key);
-          }
-          context.addMapIndex(key);
+      // [WellKnownType] could be used to for messages which have special
+      // encodings in other codecs. The set of messages which special encodings
+      // in proto3json is handled here, so we intentionally fall through to the
+      // default message handling rather than throwing.
+    }
 
-          var fieldInfo = byName[key];
-          if (fieldInfo == null && supportNamesWithUnderscores) {
-            // We don't optimize for field names with underscores, instead do a
-            // linear search for the index.
-            fieldInfo = byName.values.findFirst(
-              (FieldInfo info) => info.protoName == key,
-            );
-          }
-          if (fieldInfo == null) {
-            if (ignoreUnknownFields) {
-              return;
-            } else {
-              throw context.parseException('Unknown field name \'$key\'', key);
-            }
+    if (json is Map) {
+      final byName = meta.byName;
+
+      json.forEach((key, Object? value) {
+        if (value == null) {
+          return;
+        }
+        if (key is! String) {
+          throw context.parseException('Key was not a String', key);
+        }
+        context.addMapIndex(key);
+
+        var fieldInfo = byName[key];
+        if (fieldInfo == null && context.supportNamesWithUnderscores) {
+          // We don't optimize for field names with underscores, instead do a
+          // linear search for the index.
+          fieldInfo = byName.values.findFirst(
+            (FieldInfo info) => info.protoName == key,
+          );
+        }
+        if (fieldInfo == null) {
+          if (context.ignoreUnknownFields) {
+            return;
+          } else {
+            throw context.parseException('Unknown field name \'$key\'', key);
           }
+        }
 
-          if (PbFieldType.isMapField(fieldInfo.type)) {
-            if (value is Map) {
-              final mapFieldInfo = fieldInfo as MapFieldInfo<dynamic, dynamic>;
-              final Map fieldValues = fieldSet._ensureMapField(meta, fieldInfo);
-              value.forEach((subKey, subValue) {
-                if (subKey is! String) {
-                  throw context.parseException('Expected a String key', subKey);
-                }
-                context.addMapIndex(subKey);
-                fieldValues[decodeMapKey(
-                  subKey,
-                  mapFieldInfo.keyFieldType,
-                )] = convertProto3JsonValue(
-                  subValue,
-                  mapFieldInfo.valueFieldInfo,
-                );
-                context.popIndex();
-              });
-            } else {
-              throw context.parseException('Expected a map', value);
-            }
-          } else if (PbFieldType.isRepeated(fieldInfo.type)) {
-            if (value is List) {
-              final values = fieldSet._ensureRepeatedField(meta, fieldInfo);
-              for (var i = 0; i < value.length; i++) {
-                final entry = value[i];
-                context.addListIndex(i);
-                values.add(convertProto3JsonValue(entry, fieldInfo));
-                context.popIndex();
+        if (PbFieldType.isMapField(fieldInfo.type)) {
+          if (value is Map) {
+            final mapFieldInfo = fieldInfo as MapFieldInfo<dynamic, dynamic>;
+            final Map fieldValues = fieldSet._ensureMapField(meta, fieldInfo);
+            value.forEach((subKey, subValue) {
+              if (subKey is! String) {
+                throw context.parseException('Expected a String key', subKey);
               }
-            } else {
-              throw context.parseException('Expected a list', value);
-            }
-          } else if (PbFieldType.isGroupOrMessage(fieldInfo.type)) {
-            // TODO(sigurdm) consider a cleaner separation between parsing and
-            // merging.
-            final parsedSubMessage =
-                convertProto3JsonValue(value, fieldInfo) as GeneratedMessage;
-            final GeneratedMessage? original =
-                fieldSet._values[fieldInfo.index!];
-            if (original == null) {
-              fieldSet._setNonExtensionFieldUnchecked(
-                meta,
-                fieldInfo,
-                parsedSubMessage,
-              );
-            } else {
-              original.mergeFromMessage(parsedSubMessage);
+              context.addMapIndex(subKey);
+              fieldValues[decodeMapKey(subKey, mapFieldInfo.keyFieldType)] =
+                  convertProto3JsonValue(subValue, mapFieldInfo.valueFieldInfo);
+              context.popIndex();
+            });
+          } else {
+            throw context.parseException('Expected a map', value);
+          }
+        } else if (PbFieldType.isRepeated(fieldInfo.type)) {
+          if (value is List) {
+            final values = fieldSet._ensureRepeatedField(meta, fieldInfo);
+            for (var i = 0; i < value.length; i++) {
+              final entry = value[i];
+              context.addListIndex(i);
+              values.add(convertProto3JsonValue(entry, fieldInfo));
+              context.popIndex();
             }
           } else {
-            fieldSet._setFieldUnchecked(
+            throw context.parseException('Expected a list', value);
+          }
+        } else if (PbFieldType.isGroupOrMessage(fieldInfo.type)) {
+          // TODO(sigurdm) consider a cleaner separation between parsing and
+          // merging.
+          final parsedSubMessage =
+              convertProto3JsonValue(value, fieldInfo) as GeneratedMessage;
+          final GeneratedMessage? original = fieldSet._values[fieldInfo.index!];
+          if (original == null) {
+            fieldSet._setNonExtensionFieldUnchecked(
               meta,
               fieldInfo,
-              convertProto3JsonValue(value, fieldInfo),
+              parsedSubMessage,
             );
+          } else {
+            original.mergeFromMessage(parsedSubMessage);
           }
-          context.popIndex();
-        });
-      } else {
-        throw context.parseException('Expected JSON object', json);
-      }
+        } else {
+          fieldSet._setFieldUnchecked(
+            meta,
+            fieldInfo,
+            convertProto3JsonValue(value, fieldInfo),
+          );
+        }
+        context.popIndex();
+      });
+    } else {
+      throw context.parseException('Expected JSON object', json);
     }
   }
 
diff --git a/protobuf/pubspec.yaml b/protobuf/pubspec.yaml
index dcce0fed..162dadcc 100644
--- a/protobuf/pubspec.yaml
+++ b/protobuf/pubspec.yaml
@@ -1,5 +1,5 @@
 name: protobuf
-version: 4.2.0
+version: 5.0.0
 description: >-
   Runtime library for protocol buffers support. Use with package:protoc_plugin
   to generate Dart code for your '.proto' files.
diff --git a/protoc_plugin/CHANGELOG.md b/protoc_plugin/CHANGELOG.md
index b12de704..bf34074d 100644
--- a/protoc_plugin/CHANGELOG.md
+++ b/protoc_plugin/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 23.0.0
+
+* Update generated code for protobuf 5.0.0.
+
 ## 22.5.0
 
 * Generated files are now formatted using the Dart formatter. The code is
@@ -42,30 +46,30 @@
 
   We now parse and generate code cooresponding to the proto options
   `google.api.default_host` and `google.api.oauth_scopes`:
-  
+
   ```proto
   service Firestore {
     option (google.api.default_host) = "firestore.googleapis.com";
     option (google.api.oauth_scopes) =
         "https://www.googleapis.com/auth/cloud-platform,"
         "https://www.googleapis.com/auth/datastore";
-  
+
     ...
   ```
-  
+
   Will generate as:
-  
+
   ```dart
   class FirestoreClient extends $grpc.Client {
     /// The hostname for this service.
     static const $core.String defaultHost = 'firestore.googleapis.com';
-  
+
     /// OAuth scopes needed for the client.
     static const $core.List<$core.String> oauthScopes = [
       'https://www.googleapis.com/auth/cloud-platform',
       'https://www.googleapis.com/auth/datastore',
     ];
-  
+
     ...
   ```
 * Minimum SDK dependency bumped from 3.3.0 to 3.6.0. ([#1001])
diff --git a/protoc_plugin/lib/mixins.dart b/protoc_plugin/lib/mixins.dart
index 6d969158..73eb2ff4 100644
--- a/protoc_plugin/lib/mixins.dart
+++ b/protoc_plugin/lib/mixins.dart
@@ -38,9 +38,11 @@ class PbMixin {
   /// Typically used for static helpers since you cannot mix in static members.
   final List<String>? injectedHelpers;
 
-  /// Whether the mixin should have static methods for converting to and from
-  /// proto3 Json.
-  final bool hasProto3JsonHelpers;
+  /// The well known type name.
+  ///
+  /// Values should match enumerations in the `WellKnownType` enum from
+  /// `package:protobuf`.
+  final String? wellKnownType;
 
   const PbMixin(
     this.name, {
@@ -48,7 +50,7 @@ class PbMixin {
     this.parent,
     this.reservedNames,
     this.injectedHelpers,
-    this.hasProto3JsonHelpers = false,
+    this.wellKnownType,
   });
 
   /// Returns the mixin and its ancestors, in the order they should be applied.
diff --git a/protoc_plugin/lib/src/gen/google/protobuf/duration.pb.dart b/protoc_plugin/lib/src/gen/google/protobuf/duration.pb.dart
index 5cba2308..a60ed95b 100644
--- a/protoc_plugin/lib/src/gen/google/protobuf/duration.pb.dart
+++ b/protoc_plugin/lib/src/gen/google/protobuf/duration.pb.dart
@@ -102,8 +102,7 @@ class Duration extends $pb.GeneratedMessage with $mixin.DurationMixin {
       package:
           const $pb.PackageName(_omitMessageNames ? '' : 'google.protobuf'),
       createEmptyInstance: create,
-      toProto3Json: $mixin.DurationMixin.toProto3JsonHelper,
-      fromProto3Json: $mixin.DurationMixin.fromProto3JsonHelper)
+      wellKnownType: $mixin.WellKnownType.duration)
     ..aInt64(1, _omitFieldNames ? '' : 'seconds')
     ..a<$core.int>(2, _omitFieldNames ? '' : 'nanos', $pb.PbFieldType.O3)
     ..hasRequiredFields = false;
diff --git a/protoc_plugin/lib/src/message_generator.dart b/protoc_plugin/lib/src/message_generator.dart
index f301ea2f..d3fb0ebb 100644
--- a/protoc_plugin/lib/src/message_generator.dart
+++ b/protoc_plugin/lib/src/message_generator.dart
@@ -356,9 +356,8 @@ class MessageGenerator extends ProtobufContainer {
     final packageClause =
         package == '' ? '' : ', package: $conditionalPackageName';
     final proto3JsonClause =
-        (mixin?.hasProto3JsonHelpers ?? false)
-            ? ', toProto3Json: $mixinImportPrefix.${mixin!.name}.toProto3JsonHelper, '
-                'fromProto3Json: $mixinImportPrefix.${mixin!.name}.fromProto3JsonHelper'
+        (mixin?.wellKnownType != null)
+            ? ', wellKnownType: $mixinImportPrefix.WellKnownType.${mixin!.wellKnownType}'
             : '';
 
     final String extendedClass;
diff --git a/protoc_plugin/lib/src/well_known_types.dart b/protoc_plugin/lib/src/well_known_types.dart
index 3b322239..3d93d45e 100644
--- a/protoc_plugin/lib/src/well_known_types.dart
+++ b/protoc_plugin/lib/src/well_known_types.dart
@@ -28,7 +28,7 @@ static Any pack($protobufImportPrefix.GeneratedMessage message,
   return result;
 }''',
     ],
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'any',
   ),
   'google.protobuf.Timestamp': PbMixin(
     'TimestampMixin',
@@ -44,7 +44,7 @@ static Timestamp fromDateTime($coreImportPrefix.DateTime dateTime) {
   return result;
 }''',
     ],
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'timestamp',
   ),
   'google.protobuf.Duration': PbMixin(
     'DurationMixin',
@@ -67,71 +67,71 @@ static Duration fromDart($coreImportPrefix.Duration duration) => Duration()
   ..nanos = (duration.inMicroseconds % $coreImportPrefix.Duration.microsecondsPerSecond) * 1000;
 ''',
     ],
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'duration',
   ),
   'google.protobuf.Struct': PbMixin(
     'StructMixin',
     importFrom: _wellKnownImportPath,
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'struct',
   ),
   'google.protobuf.Value': PbMixin(
     'ValueMixin',
     importFrom: _wellKnownImportPath,
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'value',
   ),
   'google.protobuf.ListValue': PbMixin(
     'ListValueMixin',
     importFrom: _wellKnownImportPath,
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'listValue',
   ),
   'google.protobuf.DoubleValue': PbMixin(
     'DoubleValueMixin',
     importFrom: _wellKnownImportPath,
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'doubleValue',
   ),
   'google.protobuf.FloatValue': PbMixin(
     'FloatValueMixin',
     importFrom: _wellKnownImportPath,
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'floatValue',
   ),
   'google.protobuf.Int64Value': PbMixin(
     'Int64ValueMixin',
     importFrom: _wellKnownImportPath,
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'int64Value',
   ),
   'google.protobuf.UInt64Value': PbMixin(
     'UInt64ValueMixin',
     importFrom: _wellKnownImportPath,
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'uint64Value',
   ),
   'google.protobuf.Int32Value': PbMixin(
     'Int32ValueMixin',
     importFrom: _wellKnownImportPath,
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'int32Value',
   ),
   'google.protobuf.UInt32Value': PbMixin(
     'UInt32ValueMixin',
     importFrom: _wellKnownImportPath,
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'uint32Value',
   ),
   'google.protobuf.BoolValue': PbMixin(
     'BoolValueMixin',
     importFrom: _wellKnownImportPath,
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'boolValue',
   ),
   'google.protobuf.StringValue': PbMixin(
     'StringValueMixin',
     importFrom: _wellKnownImportPath,
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'stringValue',
   ),
   'google.protobuf.BytesValue': PbMixin(
     'BytesValueMixin',
     importFrom: _wellKnownImportPath,
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'bytesValue',
   ),
   'google.protobuf.FieldMask': PbMixin(
     'FieldMaskMixin',
     importFrom: _wellKnownImportPath,
-    hasProto3JsonHelpers: true,
+    wellKnownType: 'fieldMask',
   ),
 };
diff --git a/protoc_plugin/pubspec.yaml b/protoc_plugin/pubspec.yaml
index 3f6fa260..3a44417c 100644
--- a/protoc_plugin/pubspec.yaml
+++ b/protoc_plugin/pubspec.yaml
@@ -1,5 +1,5 @@
 name: protoc_plugin
-version: 22.5.0
+version: 23.0.0
 description: A protobuf protoc compiler plugin used to generate Dart code.
 repository: https://github.com/google/protobuf.dart/tree/master/protoc_plugin
 
@@ -14,7 +14,7 @@ dependencies:
   dart_style: ^3.0.0
   fixnum: ^1.0.0
   path: ^1.8.0
-  protobuf: ^4.1.0
+  protobuf: ^5.0.0
   pub_semver: ^2.2.0
 
 dev_dependencies: