diff --git a/packages/core/src/core/client.test.ts b/packages/core/src/core/client.test.ts
index ac8d9f1bd6..b7e85962a5 100644
--- a/packages/core/src/core/client.test.ts
+++ b/packages/core/src/core/client.test.ts
@@ -291,6 +291,7 @@ describe('Gemini Client (client.ts)', () => {
     it('should call chat.addHistory with the provided content', async () => {
       const mockChat = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
       } as unknown as GeminiChat;
       client['chat'] = mockChat;
 
@@ -389,6 +390,7 @@ describe('Gemini Client (client.ts)', () => {
         getHistory: mockGetHistory,
         addHistory: vi.fn(),
         setHistory: vi.fn(),
+        setTools: vi.fn(),
         getLastPromptTokenCount: vi.fn(),
       } as unknown as GeminiChat;
     });
@@ -805,6 +807,7 @@ describe('Gemini Client (client.ts)', () => {
 
       const mockChat = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       } as unknown as GeminiChat;
@@ -868,6 +871,7 @@ ${JSON.stringify(
 
       const mockChat: Partial<GeminiChat> = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       };
@@ -926,6 +930,7 @@ ${JSON.stringify(
 
       const mockChat: Partial<GeminiChat> = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       };
@@ -1003,6 +1008,7 @@ ${JSON.stringify(
 
       const mockChat: Partial<GeminiChat> = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       };
@@ -1119,6 +1125,7 @@ ${JSON.stringify(
 
       const mockChat: Partial<GeminiChat> = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       };
@@ -1167,6 +1174,7 @@ ${JSON.stringify(
 
       const mockChat: Partial<GeminiChat> = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       };
@@ -1232,6 +1240,7 @@ ${JSON.stringify(
 
       const mockChat: Partial<GeminiChat> = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       };
@@ -1289,6 +1298,7 @@ ${JSON.stringify(
 
       const mockChat: Partial<GeminiChat> = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       };
@@ -1349,6 +1359,7 @@ ${JSON.stringify(
       const lastPromptTokenCount = 900;
       const mockChat: Partial<GeminiChat> = {
         getLastPromptTokenCount: vi.fn().mockReturnValue(lastPromptTokenCount),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
       };
       client['chat'] = mockChat as GeminiChat;
@@ -1409,6 +1420,7 @@ ${JSON.stringify(
       const lastPromptTokenCount = 900;
       const mockChat: Partial<GeminiChat> = {
         getLastPromptTokenCount: vi.fn().mockReturnValue(lastPromptTokenCount),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
       };
       client['chat'] = mockChat as GeminiChat;
@@ -1467,6 +1479,7 @@ ${JSON.stringify(
           .fn()
           .mockReturnValue([{ role: 'user', parts: [{ text: 'old' }] }]),
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getChatRecordingService: vi.fn().mockReturnValue({
           getConversation: vi.fn(),
           getConversationFilePath: vi.fn(),
@@ -1479,6 +1492,7 @@ ${JSON.stringify(
           .fn()
           .mockReturnValue([{ role: 'user', parts: [{ text: 'old' }] }]),
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getChatRecordingService: vi.fn().mockReturnValue({
           getConversation: vi.fn(),
           getConversationFilePath: vi.fn(),
@@ -1616,6 +1630,7 @@ ${JSON.stringify(
       const lastPromptTokenCount = 10000;
       const mockChat: Partial<GeminiChat> = {
         getLastPromptTokenCount: vi.fn().mockReturnValue(lastPromptTokenCount),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
       };
       client['chat'] = mockChat as GeminiChat;
@@ -1689,6 +1704,7 @@ ${JSON.stringify(
 
         const mockChat: Partial<GeminiChat> = {
           addHistory: vi.fn(),
+          setTools: vi.fn(),
           getHistory: vi.fn().mockReturnValue([]),
           getLastPromptTokenCount: vi.fn(),
         };
@@ -1892,6 +1908,7 @@ ${JSON.stringify(
 
       const mockChat: Partial<GeminiChat> = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       };
@@ -1947,6 +1964,7 @@ ${JSON.stringify(
 
       const mockChat: Partial<GeminiChat> = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       };
@@ -1984,6 +2002,7 @@ ${JSON.stringify(
 
       const mockChat: Partial<GeminiChat> = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       };
@@ -2028,6 +2047,7 @@ ${JSON.stringify(
         const mockChat: Partial<GeminiChat> = {
           addHistory: vi.fn(),
           setHistory: vi.fn(),
+          setTools: vi.fn(),
           // Assume history is not empty for delta checks
           getHistory: vi
             .fn()
@@ -2443,6 +2463,7 @@ ${JSON.stringify(
           addHistory: vi.fn(),
           getHistory: vi.fn().mockReturnValue([]), // Default empty history
           setHistory: vi.fn(),
+          setTools: vi.fn(),
           getLastPromptTokenCount: vi.fn(),
         };
         client['chat'] = mockChat as GeminiChat;
@@ -2783,6 +2804,7 @@ ${JSON.stringify(
 
       const mockChat: Partial<GeminiChat> = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       };
@@ -2820,6 +2842,7 @@ ${JSON.stringify(
 
       const mockChat: Partial<GeminiChat> = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       };
@@ -2857,6 +2880,7 @@ ${JSON.stringify(
 
       const mockChat: Partial<GeminiChat> = {
         addHistory: vi.fn(),
+        setTools: vi.fn(),
         getHistory: vi.fn().mockReturnValue([]),
         getLastPromptTokenCount: vi.fn(),
       };
@@ -3069,6 +3093,7 @@ ${JSON.stringify(
 
         const mockChat: Partial<GeminiChat> = {
           addHistory: vi.fn(),
+          setTools: vi.fn(),
           getHistory: vi.fn().mockReturnValue([]),
           getLastPromptTokenCount: vi.fn(),
         };
@@ -3103,6 +3128,7 @@ ${JSON.stringify(
 
         const mockChat: Partial<GeminiChat> = {
           addHistory: vi.fn(),
+          setTools: vi.fn(),
           getHistory: vi.fn().mockReturnValue([]),
           getLastPromptTokenCount: vi.fn(),
         };
diff --git a/packages/core/src/core/client.ts b/packages/core/src/core/client.ts
index fdfa1defce..d6afeac4be 100644
--- a/packages/core/src/core/client.ts
+++ b/packages/core/src/core/client.ts
@@ -259,6 +259,10 @@ export class GeminiClient {
   private lastUsedModelId?: string;
 
   async setTools(modelId?: string): Promise<void> {
+    if (!this.chat) {
+      return;
+    }
+
     if (modelId && modelId === this.lastUsedModelId) {
       return;
     }
@@ -346,6 +350,13 @@ export class GeminiClient {
         tools,
         history,
         resumedSessionData,
+        async (modelId: string) => {
+          this.lastUsedModelId = modelId;
+          const toolRegistry = this.config.getToolRegistry();
+          const toolDeclarations =
+            toolRegistry.getFunctionDeclarations(modelId);
+          return [{ functionDeclarations: toolDeclarations }];
+        },
       );
     } catch (error) {
       await reportError(
diff --git a/packages/core/src/core/geminiChat.ts b/packages/core/src/core/geminiChat.ts
index 35a8e79855..6bea67dc0e 100644
--- a/packages/core/src/core/geminiChat.ts
+++ b/packages/core/src/core/geminiChat.ts
@@ -247,6 +247,7 @@ export class GeminiChat {
     private tools: Tool[] = [],
     private history: Content[] = [],
     resumedSessionData?: ResumedSessionData,
+    private readonly onModelChanged?: (modelId: string) => Promise<Tool[]>,
   ) {
     validateHistory(history);
     this.chatRecordingService = new ChatRecordingService(config);
@@ -581,7 +582,9 @@ export class GeminiChat {
       }
 
       // Track final request parameters for AfterModel hooks
-      await this.config.getGeminiClient().setTools(modelToUse);
+      if (this.onModelChanged) {
+        this.tools = await this.onModelChanged(modelToUse);
+      }
       lastModelToUse = modelToUse;
       lastConfig = config;
       lastContentsToUse = contentsToUse;