diff --git a/packages/vertexai/src/methods/chrome-adapter.test.ts b/packages/vertexai/src/methods/chrome-adapter.test.ts
index c350bd366c0..7e957c23614 100644
--- a/packages/vertexai/src/methods/chrome-adapter.test.ts
+++ b/packages/vertexai/src/methods/chrome-adapter.test.ts
@@ -157,7 +157,7 @@ describe('ChromeAdapter', () => {
             Promise.resolve({
               available: 'after-download'
             }),
-          create: () => {}
+          create: () => { }
         }
       } as AI;
       const downloadPromise = new Promise<AILanguageModel>(() => {
@@ -182,7 +182,7 @@ describe('ChromeAdapter', () => {
             Promise.resolve({
               available: 'after-download'
             }),
-          create: () => {}
+          create: () => { }
         }
       } as AI;
       let resolveDownload;
@@ -298,4 +298,87 @@ describe('ChromeAdapter', () => {
       });
     });
   });
+  describe('countTokens', () => {
+    it('With no initial prompts', async () => {
+      const aiProvider = {
+        languageModel: {
+          create: () => Promise.resolve({})
+        }
+      } as AI;
+      const inputText = "first";
+      const expectedCount = 10;
+      const model = {
+        countPromptTokens: _s => Promise.resolve(123),
+      } as AILanguageModel;
+      // overrides impl with stub method
+      const countPromptTokensStub = stub(model, 'countPromptTokens').resolves(expectedCount);
+      const factoryStub = stub(aiProvider.languageModel, 'create').resolves(model);
+      const adapter = new ChromeAdapter(
+        aiProvider,
+        'prefer_on_device',
+      );
+      const response = await adapter.countTokens({
+        contents: [
+          { role: 'user', parts: [{ text: inputText }] }
+        ]
+      });
+      expect(factoryStub).to.have.been.calledOnceWith({
+        // initialPrompts must be empty
+        initialPrompts: []
+      });
+      // validate count tokens gets called with the last entry from the input
+      expect(countPromptTokensStub).to.have.been.calledOnceWith({
+        role: 'user',
+        content: inputText
+      });
+      expect(await response.json()).to.deep.equal({
+        totalTokens: expectedCount
+      });
+    });
+    it('Extracts initial prompts and then does counts tokens', async () => {
+      const aiProvider = {
+        languageModel: {
+          create: () => Promise.resolve({})
+        }
+      } as AI;
+      const expectedCount = 10;
+      const model = {
+        countPromptTokens: _s => Promise.resolve(123),
+      } as AILanguageModel;
+      // overrides impl with stub method
+      const countPromptTokensStub = stub(model, 'countPromptTokens').resolves(expectedCount);
+      const factoryStub = stub(aiProvider.languageModel, 'create').resolves(model);
+      const text = ['first', 'second', 'third'];
+      const onDeviceParams = {
+        initialPrompts: [{ role: 'user', content: text[0] }]
+      } as AILanguageModelCreateOptionsWithSystemPrompt;
+      const adapter = new ChromeAdapter(
+        aiProvider,
+        'prefer_on_device',
+        onDeviceParams
+      );
+      const response = await adapter.countTokens({
+        contents: [
+          { role: 'model', parts: [{ text: text[1] }] },
+          { role: 'user', parts: [{ text: text[2] }] }
+        ]
+      });
+      expect(factoryStub).to.have.been.calledOnceWith({
+        initialPrompts: [
+          { role: 'user', content: text[0] },
+          // Asserts tail is passed as initial prompts, and
+          // role is normalized from model to assistant.
+          { role: 'assistant', content: text[1] }
+        ]
+      });
+      // validate count tokens gets called with the last entry from the input
+      expect(countPromptTokensStub).to.have.been.calledOnceWith({
+        role: 'user',
+        content: text[2]
+      });
+      expect(await response.json()).to.deep.equal({
+        totalTokens: expectedCount
+      });
+    });
+  });
 });
diff --git a/packages/vertexai/src/methods/chrome-adapter.ts b/packages/vertexai/src/methods/chrome-adapter.ts
index 01ee3ca1bff..3c61743764a 100644
--- a/packages/vertexai/src/methods/chrome-adapter.ts
+++ b/packages/vertexai/src/methods/chrome-adapter.ts
@@ -18,6 +18,7 @@
 import { isChrome } from '@firebase/util';
 import {
   Content,
+  CountTokensRequest,
   GenerateContentRequest,
   InferenceMode,
   Role
@@ -102,6 +103,20 @@ export class ChromeAdapter {
     const stream = await session.promptStreaming(prompt.content);
     return ChromeAdapter.toStreamResponse(stream);
   }
+  async countTokens(request: CountTokensRequest): Promise<Response> {
+    const options = this.onDeviceParams || {};
+    options.initialPrompts ??= [];
+    const extractedInitialPrompts = ChromeAdapter.toInitialPrompts(request.contents);
+    const currentPrompt = extractedInitialPrompts.pop()!;
+    options.initialPrompts.push(...extractedInitialPrompts);
+    const session = await this.session(options);
+    const tokenCount = await session.countPromptTokens(currentPrompt);
+    return {
+      json: async () => ({
+        totalTokens: tokenCount,
+      })
+    } as Response;
+  }
   private static isOnDeviceRequest(request: GenerateContentRequest): boolean {
     // Returns false if the prompt is empty.
     if (request.contents.length === 0) {
diff --git a/packages/vertexai/src/methods/count-tokens.test.ts b/packages/vertexai/src/methods/count-tokens.test.ts
index a3d7c99b4ba..7bff618f3e0 100644
--- a/packages/vertexai/src/methods/count-tokens.test.ts
+++ b/packages/vertexai/src/methods/count-tokens.test.ts
@@ -25,6 +25,7 @@ import { countTokens } from './count-tokens';
 import { CountTokensRequest } from '../types';
 import { ApiSettings } from '../types/internal';
 import { Task } from '../requests/request';
+import { ChromeAdapter } from './chrome-adapter';
 
 use(sinonChai);
 use(chaiAsPromised);
@@ -52,7 +53,8 @@ describe('countTokens()', () => {
     const result = await countTokens(
       fakeApiSettings,
       'model',
-      fakeRequestParams
+      fakeRequestParams,
+      new ChromeAdapter()
     );
     expect(result.totalTokens).to.equal(6);
     expect(result.totalBillableCharacters).to.equal(16);
@@ -77,7 +79,8 @@ describe('countTokens()', () => {
     const result = await countTokens(
       fakeApiSettings,
       'model',
-      fakeRequestParams
+      fakeRequestParams,
+      new ChromeAdapter()
     );
     expect(result.totalTokens).to.equal(1837);
     expect(result.totalBillableCharacters).to.equal(117);
@@ -104,7 +107,8 @@ describe('countTokens()', () => {
     const result = await countTokens(
       fakeApiSettings,
       'model',
-      fakeRequestParams
+      fakeRequestParams,
+      new ChromeAdapter()
     );
     expect(result.totalTokens).to.equal(258);
     expect(result).to.not.have.property('totalBillableCharacters');
@@ -127,7 +131,7 @@ describe('countTokens()', () => {
       json: mockResponse.json
     } as Response);
     await expect(
-      countTokens(fakeApiSettings, 'model', fakeRequestParams)
+      countTokens(fakeApiSettings, 'model', fakeRequestParams, new ChromeAdapter())
     ).to.be.rejectedWith(/404.*not found/);
     expect(mockFetch).to.be.called;
   });
diff --git a/packages/vertexai/src/methods/count-tokens.ts b/packages/vertexai/src/methods/count-tokens.ts
index c9d43a5b6fd..c6b6fab3934 100644
--- a/packages/vertexai/src/methods/count-tokens.ts
+++ b/packages/vertexai/src/methods/count-tokens.ts
@@ -22,8 +22,9 @@ import {
 } from '../types';
 import { Task, makeRequest } from '../requests/request';
 import { ApiSettings } from '../types/internal';
+import { ChromeAdapter } from './chrome-adapter';
 
-export async function countTokens(
+export async function countTokensOnCloud(
   apiSettings: ApiSettings,
   model: string,
   params: CountTokensRequest,
@@ -39,3 +40,17 @@ export async function countTokens(
   );
   return response.json();
 }
+
+export async function countTokens(
+  apiSettings: ApiSettings,
+  model: string,
+  params: CountTokensRequest,
+  chromeAdapter: ChromeAdapter,
+  requestOptions?: RequestOptions
+): Promise<CountTokensResponse> {
+  if (await chromeAdapter.isAvailable(params)) {
+    return (await chromeAdapter.countTokens(params)).json();
+  } else {
+    return countTokensOnCloud(apiSettings, model, params, requestOptions);
+  }
+}
diff --git a/packages/vertexai/src/models/generative-model.ts b/packages/vertexai/src/models/generative-model.ts
index bf72ae0be9f..60ec72be6fe 100644
--- a/packages/vertexai/src/models/generative-model.ts
+++ b/packages/vertexai/src/models/generative-model.ts
@@ -154,6 +154,6 @@ export class GenerativeModel extends VertexAIModel {
     request: CountTokensRequest | string | Array<string | Part>
   ): Promise<CountTokensResponse> {
     const formattedParams = formatGenerateContentInput(request);
-    return countTokens(this._apiSettings, this.model, formattedParams);
+    return countTokens(this._apiSettings, this.model, formattedParams, this.chromeAdapter);
   }
 }