diff --git a/packages/backend/server/src/__tests__/__snapshots__/copilot.spec.ts.md b/packages/backend/server/src/__tests__/__snapshots__/copilot.spec.ts.md
index ee137de87d..39a6e2be9a 100644
--- a/packages/backend/server/src/__tests__/__snapshots__/copilot.spec.ts.md
+++ b/packages/backend/server/src/__tests__/__snapshots__/copilot.spec.ts.md
@@ -116,6 +116,38 @@ Generated by [AVA](https://avajs.dev).
       },
     ]
 
+> should generate the final message
+
+    [
+      {
+        content: 'hello world',
+        params: {
+          word: 'world',
+        },
+        role: 'system',
+      },
+      {
+        content: 'hello',
+        params: {},
+        role: 'user',
+      },
+      {
+        content: 'world',
+        params: {},
+        role: 'assistant',
+      },
+      {
+        content: 'aaa',
+        params: {},
+        role: 'user',
+      },
+      {
+        content: 'bbb',
+        params: {},
+        role: 'assistant',
+      },
+    ]
+
 ## should revert message correctly
 
 > should have three messages before revert
diff --git a/packages/backend/server/src/__tests__/__snapshots__/copilot.spec.ts.snap b/packages/backend/server/src/__tests__/__snapshots__/copilot.spec.ts.snap
index e2b0012467..943a031e2d 100644
Binary files a/packages/backend/server/src/__tests__/__snapshots__/copilot.spec.ts.snap and b/packages/backend/server/src/__tests__/__snapshots__/copilot.spec.ts.snap differ
diff --git a/packages/backend/server/src/__tests__/copilot.e2e.ts b/packages/backend/server/src/__tests__/copilot.e2e.ts
index 3ee870cb78..3e5537a0dd 100644
--- a/packages/backend/server/src/__tests__/copilot.e2e.ts
+++ b/packages/backend/server/src/__tests__/copilot.e2e.ts
@@ -281,7 +281,7 @@ test('should fork session correctly', async t => {
   const assertForkSession = async (
     workspaceId: string,
     sessionId: string,
-    lastMessageId: string,
+    lastMessageId: string | undefined,
     error: string,
     asserter = async (x: any) => {
       const forkedSessionId = await x;
@@ -330,6 +330,27 @@ test('should fork session correctly', async t => {
     );
   }
 
+  // should be able to fork session without latestMessageId (copy all messages)
+  {
+    forkedSessionId = await assertForkSession(
+      id,
+      sessionId,
+      undefined,
+      'should be able to fork session without latestMessageId'
+    );
+  }
+
+  // should not be able to fork session with wrong latestMessageId
+  {
+    await assertForkSession(id, sessionId, 'wrong-message-id', '', async x => {
+      await t.throwsAsync(
+        x,
+        { instanceOf: Error },
+        'should not able to fork session with wrong latestMessageId'
+      );
+    });
+  }
+
   {
     const u2 = await app.signupV1('u2@affine.pro');
     await assertForkSession(id, sessionId, randomUUID(), '', async x => {
diff --git a/packages/backend/server/src/__tests__/copilot.spec.ts b/packages/backend/server/src/__tests__/copilot.spec.ts
index 233bd1584e..547878928a 100644
--- a/packages/backend/server/src/__tests__/copilot.spec.ts
+++ b/packages/backend/server/src/__tests__/copilot.spec.ts
@@ -410,6 +410,27 @@ test('should be able to fork chat session', async t => {
     'should fork new session with same params'
   );
 
+  // fork session without latestMessageId
+  const forkedSessionId3 = await session.fork({
+    userId,
+    sessionId,
+    ...commonParams,
+  });
+
+  // fork session with wrong latestMessageId
+  await t.throwsAsync(
+    session.fork({
+      userId,
+      sessionId,
+      latestMessageId: 'wrong-message-id',
+      ...commonParams,
+    }),
+    {
+      instanceOf: Error,
+    },
+    'should not able to fork new session with wrong latestMessageId'
+  );
+
   const cleanObject = (obj: any[]) =>
     JSON.parse(
       JSON.stringify(obj, (k, v) =>
@@ -436,11 +457,17 @@ test('should be able to fork chat session', async t => {
     t.snapshot(cleanObject(finalMessages), 'should generate the final message');
   }
 
+  // check third times forked session
+  {
+    const s3 = (await session.get(forkedSessionId3))!;
+    const finalMessages = s3.finish(params);
+    t.snapshot(cleanObject(finalMessages), 'should generate the final message');
+  }
+
   // check original session messages
   {
-    const s3 = (await session.get(sessionId))!;
-
-    const finalMessages = s3.finish(params);
+    const s4 = (await session.get(sessionId))!;
+    const finalMessages = s4.finish(params);
     t.snapshot(cleanObject(finalMessages), 'should generate the final message');
   }
 
diff --git a/packages/backend/server/src/__tests__/utils/copilot.ts b/packages/backend/server/src/__tests__/utils/copilot.ts
index 59f1af7b69..8ae7bb6a67 100644
--- a/packages/backend/server/src/__tests__/utils/copilot.ts
+++ b/packages/backend/server/src/__tests__/utils/copilot.ts
@@ -57,7 +57,7 @@ export async function forkCopilotSession(
   workspaceId: string,
   docId: string,
   sessionId: string,
-  latestMessageId: string
+  latestMessageId?: string
 ): Promise<string> {
   const res = await app.gql(
     `
diff --git a/packages/backend/server/src/plugins/copilot/resolver.ts b/packages/backend/server/src/plugins/copilot/resolver.ts
index 53214f6559..b70634f8c4 100644
--- a/packages/backend/server/src/plugins/copilot/resolver.ts
+++ b/packages/backend/server/src/plugins/copilot/resolver.ts
@@ -91,8 +91,9 @@ class ForkChatSessionInput {
   @Field(() => String, {
     description:
       'Identify a message in the array and keep it with all previous messages into a forked session.',
+    nullable: true,
   })
-  latestMessageId!: string;
+  latestMessageId?: string;
 }
 
 @InputType()
diff --git a/packages/backend/server/src/plugins/copilot/session.ts b/packages/backend/server/src/plugins/copilot/session.ts
index e160098b27..c2dadeb31b 100644
--- a/packages/backend/server/src/plugins/copilot/session.ts
+++ b/packages/backend/server/src/plugins/copilot/session.ts
@@ -673,16 +673,19 @@ export class ChatSessionService {
     if (!state) {
       throw new CopilotSessionNotFound();
     }
-    const lastMessageIdx = state.messages.findLastIndex(
-      ({ id, role }) =>
-        role === AiPromptRole.assistant && id === options.latestMessageId
-    );
-    if (lastMessageIdx < 0) {
-      throw new CopilotMessageNotFound({ messageId: options.latestMessageId });
+    let messages = state.messages.map(m => ({ ...m, id: undefined }));
+    if (options.latestMessageId) {
+      const lastMessageIdx = state.messages.findLastIndex(
+        ({ id, role }) =>
+          role === AiPromptRole.assistant && id === options.latestMessageId
+      );
+      if (lastMessageIdx < 0) {
+        throw new CopilotMessageNotFound({
+          messageId: options.latestMessageId,
+        });
+      }
+      messages = messages.slice(0, lastMessageIdx + 1);
     }
-    const messages = state.messages
-      .slice(0, lastMessageIdx + 1)
-      .map(m => ({ ...m, id: undefined }));
 
     const forkedState = {
       ...state,
diff --git a/packages/backend/server/src/plugins/copilot/types.ts b/packages/backend/server/src/plugins/copilot/types.ts
index ae403bf43d..9aefd70f55 100644
--- a/packages/backend/server/src/plugins/copilot/types.ts
+++ b/packages/backend/server/src/plugins/copilot/types.ts
@@ -119,7 +119,7 @@ export interface ChatSessionPromptUpdateOptions
 export interface ChatSessionForkOptions
   extends Omit<ChatSessionOptions, 'promptName'> {
   sessionId: string;
-  latestMessageId: string;
+  latestMessageId?: string;
 }
 
 export interface ChatSessionState
diff --git a/packages/backend/server/src/schema.gql b/packages/backend/server/src/schema.gql
index ff30e3190e..f9b8da63a4 100644
--- a/packages/backend/server/src/schema.gql
+++ b/packages/backend/server/src/schema.gql
@@ -703,7 +703,7 @@ input ForkChatSessionInput {
   """
   Identify a message in the array and keep it with all previous messages into a forked session.
   """
-  latestMessageId: String!
+  latestMessageId: String
   sessionId: String!
   workspaceId: String!
 }
diff --git a/packages/common/graphql/src/schema.ts b/packages/common/graphql/src/schema.ts
index 1725f57530..ccebb1b72d 100644
--- a/packages/common/graphql/src/schema.ts
+++ b/packages/common/graphql/src/schema.ts
@@ -879,7 +879,7 @@ export enum FeatureType {
 export interface ForkChatSessionInput {
   docId: Scalars['String']['input'];
   /** Identify a message in the array and keep it with all previous messages into a forked session. */
-  latestMessageId: Scalars['String']['input'];
+  latestMessageId?: InputMaybe<Scalars['String']['input']>;
   sessionId: Scalars['String']['input'];
   workspaceId: Scalars['String']['input'];
 }
diff --git a/packages/frontend/core/src/blocksuite/ai/actions/types.ts b/packages/frontend/core/src/blocksuite/ai/actions/types.ts
index 40e701c427..f690489d9d 100644
--- a/packages/frontend/core/src/blocksuite/ai/actions/types.ts
+++ b/packages/frontend/core/src/blocksuite/ai/actions/types.ts
@@ -93,7 +93,7 @@ declare global {
       docId: string;
       workspaceId: string;
       sessionId: string;
-      latestMessageId: string;
+      latestMessageId?: string;
     }
 
     interface AIImageActionOptions extends AITextActionOptions {