fix(google): add thought signature to gemini 3 pro image parts (#10462)

## Background

`generateText()` / `streamText()` doesn't pass thought signature for
image parts in response messages. That breaks multi-turn chats with
`gemini-3-pro-image-preview`

## Summary

- Gemini now supports non-PNG images in assistant messages
- Add thought signature to image parts in `response.messages`
- spec update: `LanguageModelV3File#providerMetadata` (optional field)

## Manual Verification

```ts
import { google } from '@ai-sdk/google';
import { generateText } from 'ai';
import 'dotenv/config';
import { presentImages } from '../lib/present-image';

async function main() {
  const step1 = await generateText({
    model: google('gemini-3-pro-image-preview'),
    prompt: 'Create an image of Los Angeles where all car infrastructure has been replaced with bike infrastructure, trains, pedestrian zones, and parks. The image should be photorealistic and vibrant.',
  });

  await presentImages(step1.files);

  const step2 = await generateText({
    model: google('gemini-3-pro-image-preview'),
    messages: [
      ...step1.response.messages,
      {
        role: 'user',
        content: 'Now create a variation of the image, but in the style of a watercolor painting.',
      },
    ]
  });

  await presentImages(step2.files);
}

main().catch(console.error);
```

## Related Issues

Fixes #10441
Closes #7979

Author: gr2m

.changeset/popular-hounds-boil.md

@@ -0,0 +1,7 @@
+---
+'@ai-sdk/provider': patch
+'@ai-sdk/google': patch
+'ai': patch
+---
+
+fix(google): add thought signature to gemini 3 pro image parts

examples/ai-core/src/generate-text/google-image-multi-step.ts

@@ -0,0 +1,31 @@
+import { google } from '@ai-sdk/google';
+import { generateText } from 'ai';
+
+import { presentImages } from '../lib/present-image';
+import { run } from '../lib/run';
+
+import 'dotenv/config';
+
+run(async () => {
+  const step1 = await generateText({
+    model: google('gemini-3-pro-image-preview'),
+    prompt:
+      'Create an image of Los Angeles where all car infrastructure has been replaced with bike infrastructure, trains, pedestrian zones, and parks. The image should be photorealistic and vibrant.',
+  });
+
+  await presentImages(step1.files);
+
+  const step2 = await generateText({
+    model: google('gemini-3-pro-image-preview'),
+    messages: [
+      ...step1.response.messages,
+      {
+        role: 'user',
+        content:
+          'Now create a variation of the image, but in the style of a watercolor painting.',
+      },
+    ],
+  });
+
+  await presentImages(step2.files);
+});

packages/ai/src/generate-text/generate-text.ts

@@ -964,6 +964,9 @@ function asContent<TOOLS extends ToolSet>({
           return {
             type: 'file' as const,
             file: new DefaultGeneratedFile(part),
+            ...(part.providerMetadata != null
+              ? { providerMetadata: part.providerMetadata }
+              : {}),
           };
         }
 

packages/google/src/convert-to-google-generative-ai-messages.test.ts

@@ -323,19 +323,6 @@ describe('assistant messages', () => {
     });
   });
 
-  it('should throw error for non-PNG images in assistant messages', async () => {
-    expect(() =>
-      convertToGoogleGenerativeAIMessages([
-        {
-          role: 'assistant',
-          content: [
-            { type: 'file', data: 'AAECAw==', mediaType: 'image/jpeg' },
-          ],
-        },
-      ]),
-    ).toThrow('Only PNG images are supported in assistant messages');
-  });
-
   it('should throw error for URL file data in assistant messages', async () => {
     expect(() =>
       convertToGoogleGenerativeAIMessages([

packages/google/src/convert-to-google-generative-ai-messages.ts

@@ -107,13 +107,6 @@ export function convertToGoogleGenerativeAIMessages(
                 }
 
                 case 'file': {
-                  if (part.mediaType !== 'image/png') {
-                    throw new UnsupportedFunctionalityError({
-                      functionality:
-                        'Only PNG images are supported in assistant messages',
-                    });
-                  }
-
                   if (part.data instanceof URL) {
                     throw new UnsupportedFunctionalityError({
                       functionality:
@@ -126,6 +119,7 @@ export function convertToGoogleGenerativeAIMessages(
                       mimeType: part.mediaType,
                       data: convertToBase64(part.data),
                     },
+                    thoughtSignature,
                   };
                 }
 

packages/google/src/google-generative-ai-language-model.test.ts

@@ -1411,6 +1411,7 @@ describe('doGenerate', () => {
         {
           "data": "base64encodedimagedata",
           "mediaType": "image/jpeg",
+          "providerMetadata": undefined,
           "type": "file",
         },
         {
@@ -1421,6 +1422,7 @@ describe('doGenerate', () => {
         {
           "data": "anotherbase64encodedimagedata",
           "mediaType": "image/png",
+          "providerMetadata": undefined,
           "type": "file",
         },
       ]
@@ -1473,11 +1475,13 @@ describe('doGenerate', () => {
         {
           "data": "imagedata1",
           "mediaType": "image/jpeg",
+          "providerMetadata": undefined,
           "type": "file",
         },
         {
           "data": "imagedata2",
           "mediaType": "image/png",
+          "providerMetadata": undefined,
           "type": "file",
         },
       ]
@@ -1592,11 +1596,13 @@ describe('doGenerate', () => {
         {
           "data": "validimagedata",
           "mediaType": "image/jpeg",
+          "providerMetadata": undefined,
           "type": "file",
         },
         {
           "data": "pdfdata",
           "mediaType": "application/pdf",
+          "providerMetadata": undefined,
           "type": "file",
         },
       ]

packages/google/src/google-generative-ai-language-model.ts

@@ -270,6 +270,9 @@ export class GoogleGenerativeAILanguageModel implements LanguageModelV3 {
           type: 'file' as const,
           data: part.inlineData.data,
           mediaType: part.inlineData.mimeType,
+          providerMetadata: part.thoughtSignature
+            ? { google: { thoughtSignature: part.thoughtSignature } }
+            : undefined,
         });
       }
     }
@@ -807,6 +810,7 @@ const getContentSchema = () =>
               mimeType: z.string(),
               data: z.string(),
             }),
+            thoughtSignature: z.string().nullish(),
           }),
           z.object({
             executableCode: z

packages/provider/src/language-model/v3/language-model-v3-file.ts

@@ -1,3 +1,5 @@
+import { SharedV3ProviderMetadata } from '../../shared';
+
 /**
 A file that has been generated by the model.
 Generated files as base64 encoded strings or binary data.
@@ -22,4 +24,6 @@ as base64 encoded strings. If the API returns binary data, the file data should
 be returned as binary data.
  */
   data: string | Uint8Array;
+
+  providerMetadata?: SharedV3ProviderMetadata;
 };