diff --git a/.changeset/tasty-bobcats-check.md b/.changeset/tasty-bobcats-check.md
new file mode 100644
index 0000000..7953393
--- /dev/null
+++ b/.changeset/tasty-bobcats-check.md
@@ -0,0 +1,5 @@
+---
+'ai': patch
+---
+
+StreamData: add `annotations` and `appendMessageAnnotation` support
diff --git a/packages/core/shared/parse-complex-response.test.ts b/packages/core/shared/parse-complex-response.test.ts
index 9a7d91b..3f8181c 100644
--- a/packages/core/shared/parse-complex-response.test.ts
+++ b/packages/core/shared/parse-complex-response.test.ts
@@ -231,8 +231,13 @@ describe('parseComplexResponse function', () => {
     // Execute the parser function
     const result = await parseComplexResponse({
       reader: createTestReader([
+
+        '0:"Sample text message."\n',
+        '8:[{"key":"value"}, 2]\n',
+
         '8:[{"key":"value"}, 2]\n',
         '0:"Sample text message."\n',
+
       ]),
       abortControllerRef: { current: new AbortController() },
       update: mockUpdate,
@@ -243,8 +248,14 @@ describe('parseComplexResponse function', () => {
     // check the mockUpdate call:
     expect(mockUpdate).toHaveBeenCalledTimes(2);
 
+
+    expect(mockUpdate.mock.calls[0][0]).toEqual([
+      assistantTextMessage('Sample text message.'),
+    ]);
+
     expect(mockUpdate.mock.calls[0][0]).toEqual([]);
 
+
     expect(mockUpdate.mock.calls[1][0]).toEqual([
       {
         ...assistantTextMessage('Sample text message.'),
@@ -264,6 +275,8 @@ describe('parseComplexResponse function', () => {
     });
   });
 
+
+
   it('should parse a combination of a function_call and message annotations', async () => {
     const mockUpdate = vi.fn();
 
@@ -350,4 +363,5 @@ describe('parseComplexResponse function', () => {
       data: [],
     });
   });
+
 });
diff --git a/packages/core/shared/parse-complex-response.ts b/packages/core/shared/parse-complex-response.ts
index db3de19..2fd00c2 100644
--- a/packages/core/shared/parse-complex-response.ts
+++ b/packages/core/shared/parse-complex-response.ts
@@ -15,12 +15,29 @@ type PrefixMap = {
   data: JSONValue[];
 };
 
+
+function initializeMessage({
+  generateId,
+  ...rest
+}: {
+  generateId: () => string;
+  content: string;
+  createdAt: Date;
+    annotations?: JSONValue[];
+}): Message {
+  return {
+    id: generateId(),
+    role: 'assistant',
+    ...rest
+  };
+
 function assignAnnotationsToMessage<T extends Message | null | undefined>(
   message: T,
   annotations: JSONValue[] | undefined,
 ): T {
   if (!message || !annotations || !annotations.length) return message;
   return { ...message, annotations: [...annotations] } as T;
+
 }
 
 export async function parseComplexResponse({
@@ -63,7 +80,24 @@ export async function parseComplexResponse({
           id: generateId(),
           role: 'assistant',
           content: value,
-          createdAt,
+          createdAt
+        };
+      }
+    }
+
+    if (type == 'message_annotations') {
+      if (prefixMap['text']) {
+        prefixMap['text'] = {
+          ...prefixMap['text'],
+          annotations: [...prefixMap['text'].annotations || [], ...value],
+        };
+      } else {
+        prefixMap['text'] = {
+          id: generateId(),
+          role: 'assistant',
+          content: '',
+          annotations: [...value],
+          createdAt
         };
       }
     }
diff --git a/packages/core/shared/types.ts b/packages/core/shared/types.ts
index eb7efd0..8a0fc96 100644
--- a/packages/core/shared/types.ts
+++ b/packages/core/shared/types.ts
@@ -112,7 +112,10 @@ export interface Message {
   tool_calls?: string | ToolCall[];
 
   /**
-   * Additional message-specific information added on the server via StreamData
+
+   * Additional message-specific information added on the server via StreamData 
+  * Additional message-specific information added on the server via StreamData
+
    */
   annotations?: JSONValue[] | undefined;
 }
@@ -315,7 +318,7 @@ export type UseCompletionOptions = {
 
   body?: object
 }
-=======
+
   body?: object;
 };
 
@@ -328,7 +331,7 @@ export type JSONValue =
   | { [x: string]: JSONValue }
 
   | Array<JSONValue>
-=======
+
   | Array<JSONValue>;
 
 export type AssistantMessage = {
diff --git a/packages/core/streams/ai-stream.ts b/packages/core/streams/ai-stream.ts
index 36e3615..29d5ff0 100644
--- a/packages/core/streams/ai-stream.ts
+++ b/packages/core/streams/ai-stream.ts
@@ -42,7 +42,7 @@ export interface AIStreamCallbacks {
 
 export interface AIStreamCallbacksAndOptions extends AIStreamCallbacks {
   streamData?: Data
-=======
+
 export interface AIStreamCallbacksAndOptions {
   /** `onStart`: Called once when the stream is initialized. */
   onStart?: () => Promise<void> | void;
@@ -81,10 +81,14 @@ export interface AIStreamParserOptions {
  * @returns {string | void} The parsed data or void.
  */
 export interface AIStreamParser {
+
+  (data: string, options: AIStreamParserOptions): string | void;
+
   (data: string, options: AIStreamParserOptions):
     | string
     | void
     | { isText: false; content: string };
+
 }
 
 /**
@@ -124,8 +128,13 @@ export function createEventStreamTransformer(
 
             const parsedMessage = customParser
               ? customParser(event.data, {
+
+                event: event.event
+              })
+
                   event: event.event,
                 })
+
               : event.data;
             if (parsedMessage) controller.enqueue(parsedMessage);
 
diff --git a/packages/core/streams/stream-data.ts b/packages/core/streams/stream-data.ts
index 785db17..62145bc 100644
--- a/packages/core/streams/stream-data.ts
+++ b/packages/core/streams/stream-data.ts
@@ -42,11 +42,18 @@ export class experimental_StreamData {
         }
 
         if (self.messageAnnotations.length) {
+
+          const encodedmessageAnnotations = self.encoder.encode(
+            formatStreamPart('message_annotations', self.messageAnnotations),
+          );
+          controller.enqueue(encodedmessageAnnotations);
+
           const encodedMessageAnnotations = self.encoder.encode(
             formatStreamPart('message_annotations', self.messageAnnotations),
           );
           self.messageAnnotations = [];
           controller.enqueue(encodedMessageAnnotations);
+
         }
 
         controller.enqueue(chunk);