diff --git a/packages/core/src/code_assist/codeAssist.ts b/packages/core/src/code_assist/codeAssist.ts
index c3cb9293..80d95ca9 100644
--- a/packages/core/src/code_assist/codeAssist.ts
+++ b/packages/core/src/code_assist/codeAssist.ts
@@ -12,11 +12,12 @@ import { CodeAssistServer, HttpOptions } from './server.js';
 export async function createCodeAssistContentGenerator(
   httpOptions: HttpOptions,
   authType: AuthType,
+  sessionId?: string,
 ): Promise<ContentGenerator> {
   if (authType === AuthType.LOGIN_WITH_GOOGLE) {
     const authClient = await getOauthClient();
     const projectId = await setupUser(authClient);
-    return new CodeAssistServer(authClient, projectId, httpOptions);
+    return new CodeAssistServer(authClient, projectId, httpOptions, sessionId);
   }
 
   throw new Error(`Unsupported authType: ${authType}`);
diff --git a/packages/core/src/code_assist/converter.test.ts b/packages/core/src/code_assist/converter.test.ts
index 2170c960..03f388dc 100644
--- a/packages/core/src/code_assist/converter.test.ts
+++ b/packages/core/src/code_assist/converter.test.ts
@@ -37,6 +37,7 @@ describe('converter', () => {
           labels: undefined,
           safetySettings: undefined,
           generationConfig: undefined,
+          session_id: undefined,
         },
       });
     });
@@ -59,6 +60,34 @@ describe('converter', () => {
           labels: undefined,
           safetySettings: undefined,
           generationConfig: undefined,
+          session_id: undefined,
+        },
+      });
+    });
+
+    it('should convert a request with sessionId', () => {
+      const genaiReq: GenerateContentParameters = {
+        model: 'gemini-pro',
+        contents: [{ role: 'user', parts: [{ text: 'Hello' }] }],
+      };
+      const codeAssistReq = toGenerateContentRequest(
+        genaiReq,
+        'my-project',
+        'session-123',
+      );
+      expect(codeAssistReq).toEqual({
+        model: 'gemini-pro',
+        project: 'my-project',
+        request: {
+          contents: [{ role: 'user', parts: [{ text: 'Hello' }] }],
+          systemInstruction: undefined,
+          cachedContent: undefined,
+          tools: undefined,
+          toolConfig: undefined,
+          labels: undefined,
+          safetySettings: undefined,
+          generationConfig: undefined,
+          session_id: 'session-123',
         },
       });
     });
diff --git a/packages/core/src/code_assist/converter.ts b/packages/core/src/code_assist/converter.ts
index b9b854fc..b27617c4 100644
--- a/packages/core/src/code_assist/converter.ts
+++ b/packages/core/src/code_assist/converter.ts
@@ -44,6 +44,7 @@ interface VertexGenerateContentRequest {
   labels?: Record<string, string>;
   safetySettings?: SafetySetting[];
   generationConfig?: VertexGenerationConfig;
+  session_id?: string;
 }
 
 interface VertexGenerationConfig {
@@ -114,11 +115,12 @@ export function fromCountTokenResponse(
 export function toGenerateContentRequest(
   req: GenerateContentParameters,
   project?: string,
+  sessionId?: string,
 ): CAGenerateContentRequest {
   return {
     model: req.model,
     project,
-    request: toVertexGenerateContentRequest(req),
+    request: toVertexGenerateContentRequest(req, sessionId),
   };
 }
 
@@ -136,6 +138,7 @@ export function fromGenerateContentResponse(
 
 function toVertexGenerateContentRequest(
   req: GenerateContentParameters,
+  sessionId?: string,
 ): VertexGenerateContentRequest {
   return {
     contents: toContents(req.contents),
@@ -146,6 +149,7 @@ function toVertexGenerateContentRequest(
     labels: req.config?.labels,
     safetySettings: req.config?.safetySettings,
     generationConfig: toVertexGenerationConfig(req.config),
+    session_id: sessionId,
   };
 }
 
diff --git a/packages/core/src/code_assist/server.ts b/packages/core/src/code_assist/server.ts
index 3cf0c721..f285dba8 100644
--- a/packages/core/src/code_assist/server.ts
+++ b/packages/core/src/code_assist/server.ts
@@ -48,6 +48,7 @@ export class CodeAssistServer implements ContentGenerator {
     readonly client: OAuth2Client,
     readonly projectId?: string,
     readonly httpOptions: HttpOptions = {},
+    readonly sessionId?: string,
   ) {}
 
   async generateContentStream(
@@ -55,7 +56,7 @@ export class CodeAssistServer implements ContentGenerator {
   ): Promise<AsyncGenerator<GenerateContentResponse>> {
     const resps = await this.requestStreamingPost<CaGenerateContentResponse>(
       'streamGenerateContent',
-      toGenerateContentRequest(req, this.projectId),
+      toGenerateContentRequest(req, this.projectId, this.sessionId),
       req.config?.abortSignal,
     );
     return (async function* (): AsyncGenerator<GenerateContentResponse> {
@@ -70,7 +71,7 @@ export class CodeAssistServer implements ContentGenerator {
   ): Promise<GenerateContentResponse> {
     const resp = await this.requestPost<CaGenerateContentResponse>(
       'generateContent',
-      toGenerateContentRequest(req, this.projectId),
+      toGenerateContentRequest(req, this.projectId, this.sessionId),
       req.config?.abortSignal,
     );
     return fromGenerateContentResponse(resp);
diff --git a/packages/core/src/core/client.ts b/packages/core/src/core/client.ts
index b00a689b..fe60112d 100644
--- a/packages/core/src/core/client.ts
+++ b/packages/core/src/core/client.ts
@@ -68,6 +68,7 @@ export class GeminiClient {
   async initialize(contentGeneratorConfig: ContentGeneratorConfig) {
     this.contentGenerator = await createContentGenerator(
       contentGeneratorConfig,
+      this.config.getSessionId(),
     );
     this.chat = await this.startChat();
   }
diff --git a/packages/core/src/core/contentGenerator.ts b/packages/core/src/core/contentGenerator.ts
index 4740c4ee..f0c163d2 100644
--- a/packages/core/src/core/contentGenerator.ts
+++ b/packages/core/src/core/contentGenerator.ts
@@ -101,6 +101,7 @@ export async function createContentGeneratorConfig(
 
 export async function createContentGenerator(
   config: ContentGeneratorConfig,
+  sessionId?: string,
 ): Promise<ContentGenerator> {
   const version = process.env.CLI_VERSION || process.version;
   const httpOptions = {
@@ -109,7 +110,11 @@ export async function createContentGenerator(
     },
   };
   if (config.authType === AuthType.LOGIN_WITH_GOOGLE) {
-    return createCodeAssistContentGenerator(httpOptions, config.authType);
+    return createCodeAssistContentGenerator(
+      httpOptions,
+      config.authType,
+      sessionId,
+    );
   }
 
   if (