diff --git a/packages/vertexai/src/methods/chrome-adapter.test.ts b/packages/vertexai/src/methods/chrome-adapter.test.ts
index b11fb9c937e..cce97b25f5a 100644
--- a/packages/vertexai/src/methods/chrome-adapter.test.ts
+++ b/packages/vertexai/src/methods/chrome-adapter.test.ts
@@ -307,4 +307,56 @@ describe('ChromeAdapter', () => {
       });
     });
   });
+  describe('countTokens', () => {
+    it('counts tokens from a singular input', async () => {
+      const inputText = 'first';
+      const expectedCount = 10;
+      const onDeviceParams = {
+        systemPrompt: 'be yourself'
+      } as LanguageModelCreateOptions;
+
+      // setting up stubs
+      const languageModelProvider = {
+        create: () => Promise.resolve({})
+      } as LanguageModel;
+      const languageModel = {
+        measureInputUsage: _i => Promise.resolve(123)
+      } as LanguageModel;
+      const createStub = stub(languageModelProvider, 'create').resolves(
+        languageModel
+      );
+      // overrides impl with stub method
+      const measureInputUsageStub = stub(
+        languageModel,
+        'measureInputUsage'
+      ).resolves(expectedCount);
+
+      const adapter = new ChromeAdapter(
+        languageModelProvider,
+        'prefer_on_device',
+        onDeviceParams
+      );
+      const countTokenRequest = {
+        contents: [{ role: 'user', parts: [{ text: inputText }] }]
+      } as GenerateContentRequest;
+      const response = await adapter.countTokens(countTokenRequest);
+      // Asserts initialization params are proxied.
+      expect(createStub).to.have.been.calledOnceWith(onDeviceParams);
+      // Asserts Vertex input type is mapped to Chrome type.
+      expect(measureInputUsageStub).to.have.been.calledOnceWith([
+        {
+          role: 'user',
+          content: [
+            {
+              type: 'text',
+              content: inputText
+            }
+          ]
+        }
+      ]);
+      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 10844079c03..225d2bd581d 100644
--- a/packages/vertexai/src/methods/chrome-adapter.ts
+++ b/packages/vertexai/src/methods/chrome-adapter.ts
@@ -17,6 +17,7 @@
 
 import {
   Content,
+  CountTokensRequest,
   GenerateContentRequest,
   InferenceMode,
   Part,
@@ -117,6 +118,21 @@ export class ChromeAdapter {
     } as Response;
   }
 
+  async countTokens(request: CountTokensRequest): Promise<Response> {
+    // TODO: Check if the request contains an image, and if so, throw.
+    const session = await this.createSession(
+      // TODO: normalize on-device params during construction.
+      this.onDeviceParams || {}
+    );
+    const messages = ChromeAdapter.toLanguageModelMessages(request.contents);
+    const tokenCount = await session.measureInputUsage(messages);
+    return {
+      json: async () => ({
+        totalTokens: tokenCount
+      })
+    } as Response;
+  }
+
   /**
    * Asserts inference for the given request can be performed by an on-device model.
    */
diff --git a/packages/vertexai/src/methods/count-tokens.test.ts b/packages/vertexai/src/methods/count-tokens.test.ts
index 9eccbf702fe..f77d2a36c2f 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);
@@ -55,7 +56,8 @@ describe('countTokens()', () => {
     const result = await countTokens(
       fakeApiSettings,
       'model',
-      fakeRequestParams
+      fakeRequestParams,
+      new ChromeAdapter()
     );
     expect(result.totalTokens).to.equal(6);
     expect(result.totalBillableCharacters).to.equal(16);
@@ -81,7 +83,8 @@ describe('countTokens()', () => {
     const result = await countTokens(
       fakeApiSettings,
       'model',
-      fakeRequestParams
+      fakeRequestParams,
+      new ChromeAdapter()
     );
     expect(result.totalTokens).to.equal(1837);
     expect(result.totalBillableCharacters).to.equal(117);
@@ -109,7 +112,8 @@ 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');
@@ -135,8 +139,33 @@ 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;
   });
+  it('on-device', async () => {
+    const chromeAdapter = new ChromeAdapter();
+    const isAvailableStub = stub(chromeAdapter, 'isAvailable').resolves(true);
+    const mockResponse = getMockResponse(
+      'vertexAI',
+      'unary-success-total-tokens.json'
+    );
+    const countTokensStub = stub(chromeAdapter, 'countTokens').resolves(
+      mockResponse as Response
+    );
+    const result = await countTokens(
+      fakeApiSettings,
+      'model',
+      fakeRequestParams,
+      chromeAdapter
+    );
+    expect(result.totalTokens).eq(6);
+    expect(isAvailableStub).to.be.called;
+    expect(countTokensStub).to.be.calledWith(fakeRequestParams);
+  });
 });
diff --git a/packages/vertexai/src/methods/count-tokens.ts b/packages/vertexai/src/methods/count-tokens.ts
index c9d43a5b6fd..108a4b9ee6c 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();
+  }
+
+  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 c58eb3a1497..0f7e408282c 100644
--- a/packages/vertexai/src/models/generative-model.ts
+++ b/packages/vertexai/src/models/generative-model.ts
@@ -153,6 +153,11 @@ 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
+    );
   }
 }