AI Hybrid Inference: guard against unstable browser versions

packages/ai/package.json

@@ -62,7 +62,8 @@
     "rollup": "2.79.2",
     "rollup-plugin-replace": "2.2.0",
     "rollup-plugin-typescript2": "0.36.0",
-    "typescript": "5.5.4"
+    "typescript": "5.5.4",
+    "user-agent-data-types": "0.4.2"
   },
   "repository": {
     "directory": "packages/ai",

packages/ai/src/api.ts

@@ -34,6 +34,7 @@ import { encodeInstanceIdentifier } from './helpers';
 import { GoogleAIBackend, VertexAIBackend } from './backend';
 import { ChromeAdapter } from './methods/chrome-adapter';
 import { LanguageModel } from './types/language-model';
+import { NavigatorUA } from './types/user-agent-data';
 
 export { ChatSession } from './methods/chat-session';
 export * from './requests/schema-builder';
@@ -175,6 +176,7 @@ export function getGenerativeModel(
     inCloudParams,
     new ChromeAdapter(
       window.LanguageModel as LanguageModel,
+      (window.navigator as NavigatorUA).userAgentData,
       hybridParams.mode,
       hybridParams.onDeviceParams
     ),

packages/ai/src/methods/chrome-adapter.test.ts

@@ -26,6 +26,7 @@ import {
   LanguageModelCreateOptions,
   LanguageModelMessage
 } from '../types/language-model';
+import { UADataValues } from '../types/user-agent-data';
 import { match, stub } from 'sinon';
 import { GenerateContentRequest, AIErrorCode } from '../types';
 import { Schema } from '../api';
@@ -68,6 +69,7 @@ describe('ChromeAdapter', () => {
       } as LanguageModelCreateOptions;
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        undefined,
         'prefer_on_device',
         {
           createOptions
@@ -94,15 +96,19 @@ describe('ChromeAdapter', () => {
       ).to.be.false;
     });
     it('returns false if mode is only cloud', async () => {
-      const adapter = new ChromeAdapter(undefined, 'only_in_cloud');
+      const adapter = new ChromeAdapter(undefined, undefined, 'only_in_cloud');
       expect(
         await adapter.isAvailable({
           contents: []
         })
       ).to.be.false;
     });
     it('returns false if LanguageModel API is undefined', async () => {
-      const adapter = new ChromeAdapter(undefined, 'prefer_on_device');
+      const adapter = new ChromeAdapter(
+        undefined,
+        undefined,
+        'prefer_on_device'
+      );
       expect(
         await adapter.isAvailable({
           contents: []
@@ -114,6 +120,7 @@ describe('ChromeAdapter', () => {
         {
           availability: async () => Availability.available
         } as LanguageModel,
+        undefined,
         'prefer_on_device'
       );
       expect(
@@ -122,11 +129,57 @@ describe('ChromeAdapter', () => {
         })
       ).to.be.false;
     });
+    it('returns false if unsupported browser', async () => {
+      const adapter = new ChromeAdapter(
+        {
+          availability: async () => Availability.available
+        } as LanguageModel,
+        // Defines user agent, but no supported browser.
+        {
+          brands: []
+        } as UADataValues,
+        'prefer_on_device'
+      );
+      expect(
+        await adapter.isAvailable({
+          contents: []
+        })
+      ).to.be.false;
+    });
+    it('returns true if supported browser', async () => {
+      const adapter = new ChromeAdapter(
+        {
+          availability: async () => Availability.available
+        } as LanguageModel,
+        {
+          // Defines supported browser.
+          brands: [{ brand: 'Google Chrome', version: '138' }]
+        } as UADataValues,
+        'prefer_on_device'
+      );
+      expect(
+        await adapter.isAvailable({
+          contents: [
+            {
+              role: 'user',
+              parts: [
+                {
+                  text: 'hi'
+                }
+              ]
+            }
+          ]
+        })
+      ).to.be.true;
+    });
     it('returns false if request content has "function" role', async () => {
       const adapter = new ChromeAdapter(
         {
           availability: async () => Availability.available
         } as LanguageModel,
+        {
+          brands: [{ brand: 'Google Chrome', version: '138' }]
+        } as UADataValues,
         'prefer_on_device'
       );
       expect(
@@ -145,6 +198,9 @@ describe('ChromeAdapter', () => {
         {
           availability: async () => Availability.available
         } as LanguageModel,
+        {
+          brands: [{ brand: 'Google Chrome', version: '138' }]
+        } as UADataValues,
         'prefer_on_device'
       );
       for (const mimeType of ChromeAdapter.SUPPORTED_MIME_TYPES) {
@@ -173,6 +229,9 @@ describe('ChromeAdapter', () => {
       } as LanguageModel;
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        {
+          brands: [{ brand: 'Google Chrome', version: '138' }]
+        } as UADataValues,
         'prefer_on_device'
       );
       expect(
@@ -202,6 +261,7 @@ describe('ChromeAdapter', () => {
       } as LanguageModelCreateOptions;
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        undefined,
         'prefer_on_device',
         { createOptions }
       );
@@ -225,6 +285,7 @@ describe('ChromeAdapter', () => {
       );
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        undefined,
         'prefer_on_device'
       );
       await adapter.isAvailable({
@@ -249,6 +310,7 @@ describe('ChromeAdapter', () => {
       );
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        undefined,
         'prefer_on_device'
       );
       await adapter.isAvailable({
@@ -267,6 +329,9 @@ describe('ChromeAdapter', () => {
       } as LanguageModel;
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        {
+          brands: [{ brand: 'Google Chrome', version: '138' }]
+        } as UADataValues,
         'prefer_on_device'
       );
       expect(
@@ -285,6 +350,7 @@ describe('ChromeAdapter', () => {
       ).resolves(Availability.available);
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        undefined,
         'prefer_on_device',
         {
           createOptions: {
@@ -311,7 +377,7 @@ describe('ChromeAdapter', () => {
   });
   describe('generateContent', () => {
     it('throws if Chrome API is undefined', async () => {
-      const adapter = new ChromeAdapter(undefined, 'only_on_device');
+      const adapter = new ChromeAdapter(undefined, undefined, 'only_on_device');
       await expect(
         adapter.generateContent({
           contents: []
@@ -342,6 +408,9 @@ describe('ChromeAdapter', () => {
       } as LanguageModelCreateOptions;
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        {
+          brands: [{ brand: 'Google Chrome', version: '138' }]
+        } as UADataValues,
         'prefer_on_device',
         { createOptions }
       );
@@ -389,6 +458,9 @@ describe('ChromeAdapter', () => {
       const promptStub = stub(languageModel, 'prompt').resolves(promptOutput);
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        {
+          brands: [{ brand: 'Google Chrome', version: '138' }]
+        } as UADataValues,
         'prefer_on_device'
       );
       const request = {
@@ -456,6 +528,7 @@ describe('ChromeAdapter', () => {
       };
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        undefined,
         'prefer_on_device',
         { promptOptions }
       );
@@ -489,6 +562,7 @@ describe('ChromeAdapter', () => {
       } as LanguageModel;
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        undefined,
         'prefer_on_device'
       );
       const request = {
@@ -525,6 +599,7 @@ describe('ChromeAdapter', () => {
 
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        undefined,
         'prefer_on_device'
       );
 
@@ -534,6 +609,8 @@ describe('ChromeAdapter', () => {
 
       try {
         await adapter.countTokens(countTokenRequest);
+        // eslint-disable-next-line no-throw-literal
+        throw 'unthrown';
       } catch (e) {
         // the call to countToken should be rejected with Error
         expect((e as AIError).code).to.equal(AIErrorCode.REQUEST_ERROR);
@@ -569,6 +646,7 @@ describe('ChromeAdapter', () => {
       } as LanguageModelCreateOptions;
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        undefined,
         'prefer_on_device',
         { createOptions }
       );
@@ -614,6 +692,7 @@ describe('ChromeAdapter', () => {
       );
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        undefined,
         'prefer_on_device'
       );
       const request = {
@@ -674,6 +753,7 @@ describe('ChromeAdapter', () => {
       };
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        undefined,
         'prefer_on_device',
         { promptOptions }
       );
@@ -709,6 +789,7 @@ describe('ChromeAdapter', () => {
       } as LanguageModel;
       const adapter = new ChromeAdapter(
         languageModelProvider,
+        undefined,
         'prefer_on_device'
       );
       const request = {

packages/ai/src/methods/chrome-adapter.ts

@@ -37,6 +37,7 @@ import {
   LanguageModelMessageRole,
   LanguageModelMessageType
 } from '../types/language-model';
+import { UADataValues } from '../types/user-agent-data';
 import deepMerge from 'deepmerge';
 
 /**
@@ -51,6 +52,7 @@ export class ChromeAdapter {
   private oldSession: LanguageModel | undefined;
   constructor(
     private languageModelProvider?: LanguageModel,
+    private userAgentDataProvider?: UADataValues,
     private mode?: InferenceMode,
     private onDeviceParams: OnDeviceParams = {}
   ) {}
@@ -101,7 +103,13 @@ export class ChromeAdapter {
       );
       return false;
     }
-    if (!ChromeAdapter.isOnDeviceRequest(request)) {
+    if (!this.isSupportedBrowser()) {
+      logger.debug(
+        `On-device inference unavailable because browser is unsupported.`
+      );
+      return false;
+    }
+    if (!ChromeAdapter.isSupportedRequest(request)) {
       logger.debug(
         `On-device inference unavailable because request is incompatible.`
       );
@@ -206,10 +214,23 @@ export class ChromeAdapter {
     return deepMerge(this.onDeviceParams.createOptions || {}, requestOptions);
   }
 
+  /**
+   * Guards against unstable AI API implementations.
+   */
+  private isSupportedBrowser(): boolean {
+    return !!this.userAgentDataProvider?.brands?.find(({ brand, version }) => {
+      const versionNumber = Number(version);
+      return (
+        (brand === 'Google Chrome' && versionNumber > 137) ||
+        (brand === 'Microsoft Edge' && versionNumber > 138)
+      );
+    });
+  }
+
   /**
    * Asserts inference for the given request can be performed by an on-device model.
    */
-  private static isOnDeviceRequest(request: GenerateContentRequest): boolean {
+  private static isSupportedRequest(request: GenerateContentRequest): boolean {
     // Returns false if the prompt is empty.
     if (request.contents.length === 0) {
       logger.debug('Empty prompt rejected for on-device inference.');

packages/ai/src/types/user-agent-data.ts

@@ -0,0 +1,43 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Exports the minimal subset of
+ * https://github.com/lukewarlow/user-agent-data-types
+ * required by this SDK. That package is designed to be
+ * imported using triple slash references, which are
+ * prohibited in this SDK by TSLint.
+ */
+
+export interface NavigatorUA {
+  readonly userAgentData?: NavigatorUAData;
+}
+
+interface NavigatorUABrandVersion {
+  readonly brand: string;
+  readonly version: string;
+}
+
+export interface UADataValues {
+  readonly brands?: NavigatorUABrandVersion[];
+}
+
+interface UALowEntropyJSON {
+  readonly brands: NavigatorUABrandVersion[];
+}
+
+interface NavigatorUAData extends UALowEntropyJSON {}

yarn.lock

@@ -16597,6 +16597,11 @@ use@^3.1.0:
   resolved "https://registry.npmjs.org/use/-/use-3.1.1.tgz#d50c8cac79a19fbc20f2911f56eb973f4e10070f"
   integrity sha512-cwESVXlO3url9YWlFW/TA9cshCEhtu7IKJ/p5soJ/gGpj7vbvFrAY/eIioQ6Dw23KjZhYgiIo8HOs1nQ2vr/oQ==
 
+user-agent-data-types@0.4.2:
+  version "0.4.2"
+  resolved "https://registry.npmjs.org/user-agent-data-types/-/user-agent-data-types-0.4.2.tgz#3bbd3662022c3fb9d0c2f7449b6cdd412a3f9e0d"
+  integrity sha512-jXep3kO/dGNmDOkbDa8ccp4QArgxR4I76m3QVcJ1aOF0B9toc+YtSXtX5gLdDTZXyWlpQYQrABr6L1L2GZOghw==
+
 util-deprecate@^1.0.1, util-deprecate@~1.0.1:
   version "1.0.2"
   resolved "https://registry.npmjs.org/util-deprecate/-/util-deprecate-1.0.2.tgz#450d4dc9fa70de732762fbd2d4a28981419a0ccf"