diff --git a/packages/cli/src/ui/hooks/usePrivacySettings.ts b/packages/cli/src/ui/hooks/usePrivacySettings.ts
index 64a9673812..7bf5a5ff1b 100644
--- a/packages/cli/src/ui/hooks/usePrivacySettings.ts
+++ b/packages/cli/src/ui/hooks/usePrivacySettings.ts
@@ -10,6 +10,7 @@ import {
   type CodeAssistServer,
   UserTierId,
   getCodeAssistServer,
+  debugLogger,
 } from '@google/gemini-cli-core';
 
 export interface PrivacyState {
@@ -103,7 +104,12 @@ async function getRemoteDataCollectionOptIn(
 ): Promise<boolean> {
   try {
     const resp = await server.getCodeAssistGlobalUserSetting();
-    return resp.freeTierDataCollectionOptin;
+    if (resp.freeTierDataCollectionOptin === undefined) {
+      debugLogger.warn(
+        'Warning: Code Assist API did not return freeTierDataCollectionOptin. Defaulting to true.',
+      );
+    }
+    return resp.freeTierDataCollectionOptin ?? true;
   } catch (error: unknown) {
     if (error && typeof error === 'object' && 'response' in error) {
       // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
@@ -128,5 +134,10 @@ async function setRemoteDataCollectionOptIn(
     cloudaicompanionProject: server.projectId,
     freeTierDataCollectionOptin: optIn,
   });
-  return resp.freeTierDataCollectionOptin;
+  if (resp.freeTierDataCollectionOptin === undefined) {
+    debugLogger.warn(
+      `Warning: Code Assist API did not return freeTierDataCollectionOptin. Defaulting to ${optIn}.`,
+    );
+  }
+  return resp.freeTierDataCollectionOptin ?? optIn;
 }
diff --git a/packages/core/src/code_assist/converter.test.ts b/packages/core/src/code_assist/converter.test.ts
index 21fecec547..674bbaf70e 100644
--- a/packages/core/src/code_assist/converter.test.ts
+++ b/packages/core/src/code_assist/converter.test.ts
@@ -246,7 +246,7 @@ describe('converter', () => {
       };
       const genaiRes = fromGenerateContentResponse(codeAssistRes);
       expect(genaiRes).toBeInstanceOf(GenerateContentResponse);
-      expect(genaiRes.candidates).toEqual(codeAssistRes.response.candidates);
+      expect(genaiRes.candidates).toEqual(codeAssistRes.response!.candidates);
     });
 
     it('should handle prompt feedback and usage metadata', () => {
@@ -266,10 +266,10 @@ describe('converter', () => {
       };
       const genaiRes = fromGenerateContentResponse(codeAssistRes);
       expect(genaiRes.promptFeedback).toEqual(
-        codeAssistRes.response.promptFeedback,
+        codeAssistRes.response!.promptFeedback,
       );
       expect(genaiRes.usageMetadata).toEqual(
-        codeAssistRes.response.usageMetadata,
+        codeAssistRes.response!.usageMetadata,
       );
     });
 
@@ -296,7 +296,7 @@ describe('converter', () => {
       };
       const genaiRes = fromGenerateContentResponse(codeAssistRes);
       expect(genaiRes.automaticFunctionCallingHistory).toEqual(
-        codeAssistRes.response.automaticFunctionCallingHistory,
+        codeAssistRes.response!.automaticFunctionCallingHistory,
       );
     });
 
diff --git a/packages/core/src/code_assist/converter.ts b/packages/core/src/code_assist/converter.ts
index 1d41101f31..fc163a8f02 100644
--- a/packages/core/src/code_assist/converter.ts
+++ b/packages/core/src/code_assist/converter.ts
@@ -27,6 +27,7 @@ import type {
   ToolConfig,
 } from '@google/genai';
 import { GenerateContentResponse } from '@google/genai';
+import { debugLogger } from '../utils/debugLogger.js';
 
 export interface CAGenerateContentRequest {
   model: string;
@@ -72,12 +73,12 @@ interface VertexGenerationConfig {
 }
 
 export interface CaGenerateContentResponse {
-  response: VertexGenerateContentResponse;
+  response?: VertexGenerateContentResponse;
   traceId?: string;
 }
 
 interface VertexGenerateContentResponse {
-  candidates: Candidate[];
+  candidates?: Candidate[];
   automaticFunctionCallingHistory?: Content[];
   promptFeedback?: GenerateContentResponsePromptFeedback;
   usageMetadata?: GenerateContentResponseUsageMetadata;
@@ -94,7 +95,7 @@ interface VertexCountTokenRequest {
 }
 
 export interface CaCountTokenResponse {
-  totalTokens: number;
+  totalTokens?: number;
 }
 
 export function toCountTokenRequest(
@@ -111,8 +112,13 @@ export function toCountTokenRequest(
 export function fromCountTokenResponse(
   res: CaCountTokenResponse,
 ): CountTokensResponse {
+  if (res.totalTokens === undefined) {
+    debugLogger.warn(
+      'Warning: Code Assist API did not return totalTokens. Defaulting to 0.',
+    );
+  }
   return {
-    totalTokens: res.totalTokens,
+    totalTokens: res.totalTokens ?? 0,
   };
 }
 
diff --git a/packages/core/src/code_assist/setup.ts b/packages/core/src/code_assist/setup.ts
index 895fabb6bc..dce96b9cdd 100644
--- a/packages/core/src/code_assist/setup.ts
+++ b/packages/core/src/code_assist/setup.ts
@@ -18,6 +18,7 @@ import type { AuthClient } from 'google-auth-library';
 import type { ValidationHandler } from '../fallback/types.js';
 import { ChangeAuthRequestedError } from '../utils/errors.js';
 import { ValidationRequiredError } from '../utils/googleQuotaErrors.js';
+import { debugLogger } from '../utils/debugLogger.js';
 
 export class ProjectIdRequiredError extends Error {
   constructor() {
@@ -130,11 +131,20 @@ export async function setupUser(
   }
 
   if (loadRes.currentTier) {
+    if (!loadRes.paidTier?.id && !loadRes.currentTier.id) {
+      debugLogger.warn(
+        'Warning: Code Assist API did not return a user tier ID. Defaulting to STANDARD tier.',
+      );
+    }
+
     if (!loadRes.cloudaicompanionProject) {
       if (projectId) {
         return {
           projectId,
-          userTier: loadRes.paidTier?.id ?? loadRes.currentTier.id,
+          userTier:
+            loadRes.paidTier?.id ??
+            loadRes.currentTier.id ??
+            UserTierId.STANDARD,
           userTierName: loadRes.paidTier?.name ?? loadRes.currentTier.name,
         };
       }
@@ -144,13 +154,20 @@ export async function setupUser(
     }
     return {
       projectId: loadRes.cloudaicompanionProject,
-      userTier: loadRes.paidTier?.id ?? loadRes.currentTier.id,
+      userTier:
+        loadRes.paidTier?.id ?? loadRes.currentTier.id ?? UserTierId.STANDARD,
       userTierName: loadRes.paidTier?.name ?? loadRes.currentTier.name,
     };
   }
 
   const tier = getOnboardTier(loadRes);
 
+  if (!tier.id) {
+    debugLogger.warn(
+      'Warning: Code Assist API did not return an onboarding tier ID. Defaulting to STANDARD tier.',
+    );
+  }
+
   let onboardReq: OnboardUserRequest;
   if (tier.id === UserTierId.FREE) {
     // The free tier uses a managed google cloud project. Setting a project in the `onboardUser` request causes a `Precondition Failed` error.
@@ -183,7 +200,7 @@ export async function setupUser(
     if (projectId) {
       return {
         projectId,
-        userTier: tier.id,
+        userTier: tier.id ?? UserTierId.STANDARD,
         userTierName: tier.name,
       };
     }
@@ -193,7 +210,7 @@ export async function setupUser(
 
   return {
     projectId: lroRes.response.cloudaicompanionProject.id,
-    userTier: tier.id,
+    userTier: tier.id ?? UserTierId.STANDARD,
     userTierName: tier.name,
   };
 }
diff --git a/packages/core/src/code_assist/types.ts b/packages/core/src/code_assist/types.ts
index 0e2f353aa3..79932efc02 100644
--- a/packages/core/src/code_assist/types.ts
+++ b/packages/core/src/code_assist/types.ts
@@ -60,7 +60,7 @@ export interface LoadCodeAssistResponse {
  * GeminiUserTier reflects the structure received from the CodeAssist when calling LoadCodeAssist.
  */
 export interface GeminiUserTier {
-  id: UserTierId;
+  id?: UserTierId;
   name?: string;
   description?: string;
   // This value is used to declare whether a given tier requires the user to configure the project setting on the IDE settings or not.
@@ -79,10 +79,10 @@ export interface GeminiUserTier {
  * @param tierName name of the tier.
  */
 export interface IneligibleTier {
-  reasonCode: IneligibleTierReasonCode;
-  reasonMessage: string;
-  tierId: UserTierId;
-  tierName: string;
+  reasonCode?: IneligibleTierReasonCode;
+  reasonMessage?: string;
+  tierId?: UserTierId;
+  tierName?: string;
   validationErrorMessage?: string;
   validationUrl?: string;
   validationUrlLinkText?: string;
@@ -127,7 +127,7 @@ export type UserTierId = (typeof UserTierId)[keyof typeof UserTierId] | string;
  * privacy notice.
  */
 export interface PrivacyNotice {
-  showNotice: boolean;
+  showNotice?: boolean;
   noticeText?: string;
 }
 
@@ -145,7 +145,7 @@ export interface OnboardUserRequest {
  * http://google3/google/longrunning/operations.proto;rcl=698857719;l=107
  */
 export interface LongRunningOperationResponse {
-  name: string;
+  name?: string;
   done?: boolean;
   response?: OnboardUserResponse;
 }
@@ -157,8 +157,8 @@ export interface LongRunningOperationResponse {
 export interface OnboardUserResponse {
   // tslint:disable-next-line:enforce-name-casing This is the name of the field in the proto.
   cloudaicompanionProject?: {
-    id: string;
-    name: string;
+    id?: string;
+    name?: string;
   };
 }
 
@@ -195,7 +195,7 @@ export interface SetCodeAssistGlobalUserSettingRequest {
 
 export interface CodeAssistGlobalUserSettingResponse {
   cloudaicompanionProject?: string;
-  freeTierDataCollectionOptin: boolean;
+  freeTierDataCollectionOptin?: boolean;
 }
 
 /**