2 files changed, 10 insertions, 3 deletions
diff --git a/packages/core/src/core/turn.test.ts b/packages/core/src/core/turn.test.ts
index 2217e5da..aeb30229 100644
--- a/packages/core/src/core/turn.test.ts
+++ b/packages/core/src/core/turn.test.ts
@@ -239,6 +239,8 @@ describe('Turn', () => {
           candidates: [{ content: { parts: [{ text: 'First response' }] } }],
           usageMetadata: mockMetadata1,
         } as unknown as GenerateContentResponse;
+        // Add a small delay to ensure apiTimeMs is > 0
+        await new Promise((resolve) => setTimeout(resolve, 10));
         yield {
           functionCalls: [{ name: 'aTool' }],
           usageMetadata: mockMetadata2,
@@ -262,7 +264,10 @@ describe('Turn', () => {
       expect(metadataEvent.type).toBe(GeminiEventType.UsageMetadata);
 
       // The value should be the *last* metadata object received.
-      expect(metadataEvent.value).toEqual(mockMetadata2);
+      expect(metadataEvent.value).toEqual(
+        expect.objectContaining(mockMetadata2),
+      );
+      expect(metadataEvent.value.apiTimeMs).toBeGreaterThan(0);
 
       // Also check the public getter
       expect(turn.getUsageMetadata()).toEqual(mockMetadata2);
diff --git a/packages/core/src/core/turn.ts b/packages/core/src/core/turn.ts
index 34e4a494..71c02d83 100644
--- a/packages/core/src/core/turn.ts
+++ b/packages/core/src/core/turn.ts
@@ -104,7 +104,7 @@ export type ServerGeminiChatCompressedEvent = {
 
 export type ServerGeminiUsageMetadataEvent = {
   type: GeminiEventType.UsageMetadata;
-  value: GenerateContentResponseUsageMetadata;
+  value: GenerateContentResponseUsageMetadata & { apiTimeMs?: number };
 };
 
 // The original union type, now composed of the individual types
@@ -137,6 +137,7 @@ export class Turn {
     req: PartListUnion,
     signal: AbortSignal,
   ): AsyncGenerator<ServerGeminiStreamEvent> {
+    const startTime = Date.now();
     try {
       const responseStream = await this.chat.sendMessageStream({
         message: req,
@@ -174,9 +175,10 @@ export class Turn {
       }
 
       if (this.lastUsageMetadata) {
+        const durationMs = Date.now() - startTime;
         yield {
           type: GeminiEventType.UsageMetadata,
-          value: this.lastUsageMetadata,
+          value: { ...this.lastUsageMetadata, apiTimeMs: durationMs },
         };
       }
     } catch (error) {