Backport: fix(google): use VALIDATED function calling mode when any tool has strict:true (#13098)

This is an automated backport of #12967 to the release-v6.0 branch. FYI
@sleitor

Co-authored-by: Dmitrii <sleitor@list.ru>
Co-authored-by: Dmitrii Troitskii <jsleitor@gmail.com>

Author: vercel-ai-sdk[bot]

.changeset/google-validated-strict-tools.md

@@ -0,0 +1,5 @@
+---
+'@ai-sdk/google': patch
+---
+
+fix(google): use VALIDATED function calling mode when any tool has strict:true

packages/google/src/google-prepare-tools.test.ts

@@ -560,3 +560,98 @@ it('should add warnings for google maps on unsupported models', () => {
     ]
   `);
 });
+
+it('should use VALIDATED mode when any function tool has strict: true', () => {
+  const result = prepareTools({
+    tools: [
+      {
+        type: 'function',
+        name: 'createMeeting',
+        description: 'Create a meeting',
+        inputSchema: {
+          type: 'object',
+          properties: { title: { type: 'string' } },
+          required: ['title'],
+          additionalProperties: false,
+        },
+        strict: true,
+      },
+    ],
+    modelId: 'gemini-3-flash-preview',
+  });
+  expect(result.toolConfig).toEqual({
+    functionCallingConfig: { mode: 'VALIDATED' },
+  });
+  expect(result.toolWarnings).toEqual([]);
+});
+
+it('should use VALIDATED mode with toolChoice auto when strict: true', () => {
+  const result = prepareTools({
+    tools: [
+      {
+        type: 'function',
+        name: 'getWeather',
+        description: 'Get weather',
+        inputSchema: {
+          type: 'object',
+          properties: { city: { type: 'string' } },
+          required: ['city'],
+          additionalProperties: false,
+        },
+        strict: true,
+      },
+    ],
+    toolChoice: { type: 'auto' },
+    modelId: 'gemini-3-flash-preview',
+  });
+  expect(result.toolConfig).toEqual({
+    functionCallingConfig: { mode: 'VALIDATED' },
+  });
+});
+
+it('should use VALIDATED mode with toolChoice required when strict: true', () => {
+  const result = prepareTools({
+    tools: [
+      {
+        type: 'function',
+        name: 'getWeather',
+        description: 'Get weather',
+        inputSchema: {
+          type: 'object',
+          properties: { city: { type: 'string' } },
+          required: ['city'],
+          additionalProperties: false,
+        },
+        strict: true,
+      },
+    ],
+    toolChoice: { type: 'required' },
+    modelId: 'gemini-3-flash-preview',
+  });
+  expect(result.toolConfig).toEqual({
+    functionCallingConfig: { mode: 'VALIDATED' },
+  });
+});
+
+it('should use AUTO mode when no tools have strict: true', () => {
+  const result = prepareTools({
+    tools: [
+      {
+        type: 'function',
+        name: 'getWeather',
+        description: 'Get weather',
+        inputSchema: {
+          type: 'object',
+          properties: { city: { type: 'string' } },
+          required: ['city'],
+          additionalProperties: false,
+        },
+      },
+    ],
+    toolChoice: { type: 'auto' },
+    modelId: 'gemini-3-flash-preview',
+  });
+  expect(result.toolConfig).toEqual({
+    functionCallingConfig: { mode: 'AUTO' },
+  });
+});

packages/google/src/google-prepare-tools.ts

@@ -31,7 +31,7 @@ export function prepareTools({
     | undefined
     | {
         functionCallingConfig: {
-          mode: 'AUTO' | 'NONE' | 'ANY';
+          mode: 'AUTO' | 'NONE' | 'ANY' | 'VALIDATED';
           allowedFunctionNames?: string[];
         };
       };
@@ -189,6 +189,7 @@ export function prepareTools({
   }
 
   const functionDeclarations = [];
+  let hasStrictTools = false;
   for (const tool of tools) {
     switch (tool.type) {
       case 'function':
@@ -197,6 +198,9 @@ export function prepareTools({
           description: tool.description ?? '',
           parameters: convertJSONSchemaToOpenAPISchema(tool.inputSchema),
         });
+        if (tool.strict === true) {
+          hasStrictTools = true;
+        }
         break;
       default:
         toolWarnings.push({ type: 'unsupported-tool', tool });
@@ -207,7 +211,9 @@ export function prepareTools({
   if (toolChoice == null) {
     return {
       tools: [{ functionDeclarations }],
-      toolConfig: undefined,
+      toolConfig: hasStrictTools
+        ? { functionCallingConfig: { mode: 'VALIDATED' } }
+        : undefined,
       toolWarnings,
     };
   }
@@ -218,7 +224,11 @@ export function prepareTools({
     case 'auto':
       return {
         tools: [{ functionDeclarations }],
-        toolConfig: { functionCallingConfig: { mode: 'AUTO' } },
+        toolConfig: {
+          functionCallingConfig: {
+            mode: hasStrictTools ? 'VALIDATED' : 'AUTO',
+          },
+        },
         toolWarnings,
       };
     case 'none':
@@ -230,15 +240,19 @@ export function prepareTools({
     case 'required':
       return {
         tools: [{ functionDeclarations }],
-        toolConfig: { functionCallingConfig: { mode: 'ANY' } },
+        toolConfig: {
+          functionCallingConfig: {
+            mode: hasStrictTools ? 'VALIDATED' : 'ANY',
+          },
+        },
         toolWarnings,
       };
     case 'tool':
       return {
         tools: [{ functionDeclarations }],
         toolConfig: {
           functionCallingConfig: {
-            mode: 'ANY',
+            mode: hasStrictTools ? 'VALIDATED' : 'ANY',
             allowedFunctionNames: [toolChoice.toolName],
           },
         },