diff --git a/ably.d.ts b/ably.d.ts
index b8e85c6a4..b4bf04ef5 100644
--- a/ably.d.ts
+++ b/ably.d.ts
@@ -2335,12 +2335,104 @@ export interface Message {
    * Timestamp of when the message was received by Ably, as milliseconds since the Unix epoch.
    */
   timestamp?: number;
+  /**
+   * The action type of the message, one of the {@link MessageAction} enum values.
+   */
+  action?: MessageAction;
+  /**
+   * This message's unique serial.
+   */
+  serial?: string;
+  /**
+   * The serial of the message that this message is a reference to.
+   */
+  refSerial?: string;
+  /**
+   * The type of reference this message is, in relation to the message it references.
+   */
+  refType?: string;
+  /**
+   * If an `update` operation was applied to this message, this will be the timestamp the update occurred.
+   */
+  updatedAt?: number;
+  /**
+   * If a `deletion` operation was applied to this message, this will be the timestamp the deletion occurred.
+   */
+  deletedAt?: number;
+  /**
+   * If this message resulted from an operation, this will contain the operation details.
+   */
+  operation?: Operation;
 }
 
+/**
+ * Contains the details of an operation, such as update or deletion, supplied by the actioning client.
+ */
+export interface Operation {
+  /**
+   * The client ID of the client that initiated the operation.
+   */
+  clientId?: string;
+  /**
+   * The description provided by the client that initiated the operation.
+   */
+  description?: string;
+  /**
+   * A JSON object of string key-value pairs that may contain metadata associated with the operation.
+   */
+  metadata?: Record<string, string>;
+}
+
+/**
+ * The namespace containing the different types of message actions.
+ */
+declare namespace MessageActions {
+  /**
+   * Message action has not been set.
+   */
+  type MESSAGE_UNSET = 'message.unset';
+  /**
+   * Message action for a newly created message.
+   */
+  type MESSAGE_CREATE = 'message.create';
+  /**
+   * Message action for an updated message.
+   */
+  type MESSAGE_UPDATE = 'message.update';
+  /**
+   * Message action for a deleted message.
+   */
+  type MESSAGE_DELETE = 'message.delete';
+  /**
+   * Message action for a newly created annotation.
+   */
+  type ANNOTATION_CREATE = 'annotation.create';
+  /**
+   * Message action for a deleted annotation.
+   */
+  type ANNOTATION_DELETE = 'annotation.delete';
+  /**
+   * Message action for a meta-message that contains channel occupancy information.
+   */
+  type META_OCCUPANCY = 'meta.occupancy';
+}
+
+/**
+ * Describes the possible action types used on an {@link Message}.
+ */
+export type MessageAction =
+  | MessageActions.MESSAGE_UNSET
+  | MessageActions.MESSAGE_CREATE
+  | MessageActions.MESSAGE_UPDATE
+  | MessageActions.MESSAGE_DELETE
+  | MessageActions.ANNOTATION_CREATE
+  | MessageActions.ANNOTATION_DELETE
+  | MessageActions.META_OCCUPANCY;
+
 /**
  * A message received from Ably.
  */
-export type InboundMessage = Message & Required<Pick<Message, 'id' | 'timestamp'>>;
+export type InboundMessage = Message & Required<Pick<Message, 'id' | 'timestamp' | 'serial' | 'action'>>;
 
 /**
  * Static utilities related to messages.
diff --git a/package.json b/package.json
index 0a8271645..0a82a90ec 100644
--- a/package.json
+++ b/package.json
@@ -139,6 +139,7 @@
     "grunt": "grunt",
     "test": "npm run test:node",
     "test:node": "npm run build:node && npm run build:push && mocha",
+    "test:grep": "npm run build:node && npm run build:push && mocha --grep",
     "test:node:skip-build": "mocha",
     "test:webserver": "grunt test:webserver",
     "test:playwright": "node test/support/runPlaywrightTests.js",
diff --git a/scripts/moduleReport.ts b/scripts/moduleReport.ts
index 25daba894..aacec5a00 100644
--- a/scripts/moduleReport.ts
+++ b/scripts/moduleReport.ts
@@ -6,7 +6,7 @@ import { gzip } from 'zlib';
 import Table from 'cli-table';
 
 // The maximum size we allow for a minimal useful Realtime bundle (i.e. one that can subscribe to a channel)
-const minimalUsefulRealtimeBundleSizeThresholdsKiB = { raw: 98, gzip: 30 };
+const minimalUsefulRealtimeBundleSizeThresholdsKiB = { raw: 100, gzip: 31 };
 
 const baseClientNames = ['BaseRest', 'BaseRealtime'];
 
diff --git a/src/common/lib/client/restchannel.ts b/src/common/lib/client/restchannel.ts
index 3138e8611..e27133c6e 100644
--- a/src/common/lib/client/restchannel.ts
+++ b/src/common/lib/client/restchannel.ts
@@ -2,12 +2,12 @@ import * as Utils from '../util/utils';
 import Logger from '../util/logger';
 import RestPresence from './restpresence';
 import Message, {
-  fromValues as messageFromValues,
-  fromValuesArray as messagesFromValuesArray,
   encodeArray as encodeMessagesArray,
   serialize as serializeMessage,
   getMessagesSize,
   CipherOptions,
+  fromValues as messageFromValues,
+  fromValuesArray as messagesFromValuesArray,
 } from '../types/message';
 import ErrorInfo from '../types/errorinfo';
 import { PaginatedResult } from './paginatedresource';
diff --git a/src/common/lib/types/defaultmessage.ts b/src/common/lib/types/defaultmessage.ts
index dfc4a02b1..79fffccf5 100644
--- a/src/common/lib/types/defaultmessage.ts
+++ b/src/common/lib/types/defaultmessage.ts
@@ -1,10 +1,11 @@
 import Message, {
   CipherOptions,
-  fromEncoded,
-  fromEncodedArray,
-  encode,
   decode,
+  encode,
   EncodingDecodingContext,
+  fromEncoded,
+  fromEncodedArray,
+  fromValues,
 } from './message';
 import * as API from '../../../../ably';
 import Platform from 'common/platform';
@@ -25,8 +26,8 @@ export class DefaultMessage extends Message {
   }
 
   // Used by tests
-  static fromValues(values: unknown): Message {
-    return Object.assign(new Message(), values);
+  static fromValues(values: Message | Record<string, unknown>, options?: { stringifyAction?: boolean }): Message {
+    return fromValues(values, options);
   }
 
   // Used by tests
diff --git a/src/common/lib/types/message.ts b/src/common/lib/types/message.ts
index 7cc8b80ac..f0d9c5394 100644
--- a/src/common/lib/types/message.ts
+++ b/src/common/lib/types/message.ts
@@ -9,6 +9,30 @@ import * as API from '../../../../ably';
 import { IUntypedCryptoStatic } from 'common/types/ICryptoStatic';
 import { MsgPack } from 'common/types/msgpack';
 
+const MessageActionArray: API.MessageAction[] = [
+  'message.unset',
+  'message.create',
+  'message.update',
+  'message.delete',
+  'annotation.create',
+  'annotation.delete',
+  'meta.occupancy',
+];
+
+const MessageActionMap = new Map<API.MessageAction, number>(MessageActionArray.map((action, index) => [action, index]));
+
+const ReverseMessageActionMap = new Map<number, API.MessageAction>(
+  MessageActionArray.map((action, index) => [index, action]),
+);
+
+function toMessageActionString(actionNumber: number): API.MessageAction | undefined {
+  return ReverseMessageActionMap.get(actionNumber);
+}
+
+function toMessageActionNumber(messageAction?: API.MessageAction): number | undefined {
+  return messageAction ? MessageActionMap.get(messageAction) : undefined;
+}
+
 export type CipherOptions = {
   channelCipher: {
     encrypt: Function;
@@ -82,7 +106,7 @@ export async function fromEncoded(
   encoded: unknown,
   inputOptions?: API.ChannelOptions,
 ): Promise<Message> {
-  const msg = fromValues(encoded);
+  const msg = fromValues(encoded as Message | Record<string, unknown>, { stringifyAction: true });
   const options = normalizeCipherOptions(Crypto, logger, inputOptions ?? null);
   /* if decoding fails at any point, catch and return the message decoded to
    * the fullest extent possible */
@@ -260,7 +284,7 @@ export async function fromResponseBody(
   }
 
   for (let i = 0; i < body.length; i++) {
-    const msg = (body[i] = fromValues(body[i]));
+    const msg = (body[i] = fromValues(body[i], { stringifyAction: true }));
     try {
       await decode(msg, options);
     } catch (e) {
@@ -270,14 +294,22 @@ export async function fromResponseBody(
   return body;
 }
 
-export function fromValues(values: unknown): Message {
+export function fromValues(
+  values: Message | Record<string, unknown>,
+  options?: { stringifyAction?: boolean },
+): Message {
+  const stringifyAction = options?.stringifyAction;
+  if (stringifyAction) {
+    const action = toMessageActionString(values.action as number) || values.action;
+    return Object.assign(new Message(), { ...values, action });
+  }
   return Object.assign(new Message(), values);
 }
 
 export function fromValuesArray(values: unknown[]): Message[] {
   const count = values.length,
     result = new Array(count);
-  for (let i = 0; i < count; i++) result[i] = fromValues(values[i]);
+  for (let i = 0; i < count; i++) result[i] = fromValues(values[i] as Record<string, unknown>);
   return result;
 }
 
@@ -304,6 +336,13 @@ class Message {
   encoding?: string | null;
   extras?: any;
   size?: number;
+  action?: API.MessageAction | number;
+  serial?: string;
+  refSerial?: string;
+  refType?: string;
+  updatedAt?: number;
+  deletedAt?: number;
+  operation?: API.Operation;
 
   /**
    * Overload toJSON() to intercept JSON.stringify()
@@ -334,6 +373,13 @@ class Message {
       connectionId: this.connectionId,
       connectionKey: this.connectionKey,
       extras: this.extras,
+      serial: this.serial,
+      action: toMessageActionNumber(this.action as API.MessageAction) || this.action,
+      refSerial: this.refSerial,
+      refType: this.refType,
+      updatedAt: this.updatedAt,
+      deletedAt: this.deletedAt,
+      operation: this.operation,
       encoding,
       data,
     };
@@ -355,6 +401,14 @@ class Message {
       else result += '; data (json)=' + JSON.stringify(this.data);
     }
     if (this.extras) result += '; extras=' + JSON.stringify(this.extras);
+
+    if (this.action) result += '; action=' + this.action;
+    if (this.serial) result += '; serial=' + this.serial;
+    if (this.refSerial) result += '; refSerial=' + this.refSerial;
+    if (this.refType) result += '; refType=' + this.refType;
+    if (this.updatedAt) result += '; updatedAt=' + this.updatedAt;
+    if (this.deletedAt) result += '; deletedAt=' + this.deletedAt;
+    if (this.operation) result += '; operation=' + JSON.stringify(this.operation);
     result += ']';
     return result;
   }
diff --git a/src/common/lib/types/protocolmessage.ts b/src/common/lib/types/protocolmessage.ts
index eaa622a8d..ccb15841f 100644
--- a/src/common/lib/types/protocolmessage.ts
+++ b/src/common/lib/types/protocolmessage.ts
@@ -81,16 +81,26 @@ export function fromDeserialized(
   presenceMessagePlugin: PresenceMessagePlugin | null,
 ): ProtocolMessage {
   const error = deserialized.error;
-  if (error) deserialized.error = ErrorInfo.fromValues(error as ErrorInfo);
+  if (error) {
+    deserialized.error = ErrorInfo.fromValues(error as ErrorInfo);
+  }
+
   const messages = deserialized.messages as Message[];
-  if (messages) for (let i = 0; i < messages.length; i++) messages[i] = messageFromValues(messages[i]);
+  if (messages) {
+    for (let i = 0; i < messages.length; i++) {
+      messages[i] = messageFromValues(messages[i], { stringifyAction: true });
+    }
+  }
 
   const presence = presenceMessagePlugin ? (deserialized.presence as PresenceMessage[]) : undefined;
   if (presenceMessagePlugin) {
-    if (presence && presenceMessagePlugin)
-      for (let i = 0; i < presence.length; i++)
+    if (presence && presenceMessagePlugin) {
+      for (let i = 0; i < presence.length; i++) {
         presence[i] = presenceMessagePlugin.presenceMessageFromValues(presence[i], true);
+      }
+    }
   }
+
   return Object.assign(new ProtocolMessage(), { ...deserialized, presence });
 }
 
diff --git a/test/realtime/crypto.test.js b/test/realtime/crypto.test.js
index 14cb65330..18df2f11e 100644
--- a/test/realtime/crypto.test.js
+++ b/test/realtime/crypto.test.js
@@ -395,6 +395,7 @@ define(['ably', 'shared_helper', 'async', 'chai'], function (Ably, Helper, async
               helper.recordPrivateApi('call.msgpack.decode');
               var messageFromMsgpack = Message.fromValues(
                 msgpack.decode(BufferUtils.base64Decode(msgpackEncodedMessage)),
+                { stringifyAction: true },
               );
 
               try {
@@ -439,6 +440,7 @@ define(['ably', 'shared_helper', 'async', 'chai'], function (Ably, Helper, async
               helper.recordPrivateApi('call.msgpack.decode');
               var messageFromMsgpack = Message.fromValues(
                 msgpack.decode(BufferUtils.base64Decode(msgpackEncodedMessage)),
+                { stringifyAction: true },
               );
 
               try {
diff --git a/test/realtime/message.test.js b/test/realtime/message.test.js
index 6d0fe8f7c..6cb2cfd0a 100644
--- a/test/realtime/message.test.js
+++ b/test/realtime/message.test.js
@@ -4,6 +4,7 @@ define(['ably', 'shared_helper', 'async', 'chai'], function (Ably, Helper, async
   var expect = chai.expect;
   let config = Ably.Realtime.Platform.Config;
   var createPM = Ably.protocolMessageFromDeserialized;
+  var Message = Ably.Realtime.Message;
 
   var publishIntervalHelper = function (currentMessageNum, channel, dataFn, onPublish) {
     return function () {
@@ -1271,6 +1272,56 @@ define(['ably', 'shared_helper', 'async', 'chai'], function (Ably, Helper, async
         channel.publish('end', null);
       });
     });
+    /**
+     * @spec TM2j
+     */
+    describe('DefaultMessage.fromValues stringify action', function () {
+      const testCases = [
+        {
+          description: 'should stringify the numeric action',
+          action: 1,
+          options: { stringifyAction: true },
+          expectedString: '[Message; action=message.create]',
+          expectedJSON: { action: 1 },
+        },
+        {
+          description: 'should not stringify the numeric action',
+          action: 1,
+          options: { stringifyAction: false },
+          expectedString: '[Message; action=1]',
+          expectedJSON: { action: 1 },
+        },
+        {
+          description: 'should accept an already stringified action',
+          action: 'message.update',
+          options: { stringifyAction: true },
+          expectedString: '[Message; action=message.update]',
+          expectedJSON: { action: 2 },
+        },
+        {
+          description: 'should handle no action provided',
+          action: undefined,
+          options: { stringifyAction: true },
+          expectedString: '[Message]',
+          expectedJSON: { action: undefined },
+        },
+        {
+          description: 'should handle unknown action provided',
+          action: 10,
+          options: { stringifyAction: true },
+          expectedString: '[Message; action=10]',
+          expectedJSON: { action: 10 },
+        },
+      ];
+      testCases.forEach(({ description, action, options, expectedString, expectedJSON }) => {
+        it(description, function () {
+          const values = { action };
+          const message = Message.fromValues(values, options);
+          expect(message.toString()).to.equal(expectedString);
+          expect(message.toJSON()).to.deep.contains(expectedJSON);
+        });
+      });
+    });
 
     /**
      * @spec RTS5
diff --git a/test/support/runPlaywrightTests.js b/test/support/runPlaywrightTests.js
index edbcc1531..5ff2d9106 100644
--- a/test/support/runPlaywrightTests.js
+++ b/test/support/runPlaywrightTests.js
@@ -68,14 +68,20 @@ const runTests = async (browserType) => {
 
     // Use page.evaluate to add these functions as event listeners to the 'testLog' and 'testResult' Custom Events.
     // These events are fired by the custom mocha reporter in playwrightSetup.js
-    page.evaluate(() => {
+    const grep = process.env.MOCHA_GREP;
+    page.evaluate((grep) => {
       window.addEventListener('testLog', ({ type, detail }) => {
         onTestLog({ type, detail });
       });
       window.addEventListener('testResult', ({ type, detail }) => {
         onTestResult({ type, detail });
       });
-    });
+      // Set grep pattern in the browser context
+      // allows easy filtering of tests.
+      if (grep) {
+        window.mocha.grep(new RegExp(grep));
+      }
+    }, grep);
   });
 };