diff --git a/extensions/google/transport-stream.test.ts b/extensions/google/transport-stream.test.ts
index b19f6ca0eb0b..b9bdd9e1a9bf 100644
--- a/extensions/google/transport-stream.test.ts
+++ b/extensions/google/transport-stream.test.ts
@@ -371,19 +371,14 @@ describe("google transport stream", () => {
     });
 
     const payload = parseRequestJsonBody(init);
-    expect(payload.systemInstruction).toEqual({
-      parts: [{ text: "Follow policy." }],
-    });
     expect(payload.cachedContent).toBe("cachedContents/request-cache");
+    expect(payload.systemInstruction).toBeUndefined();
+    expect(payload.tools).toBeUndefined();
+    expect(payload.toolConfig).toBeUndefined();
     expect((payload.generationConfig as { thinkingConfig?: unknown }).thinkingConfig).toEqual({
       includeThoughts: true,
       thinkingLevel: "HIGH",
     });
-    expect(
-      (payload.toolConfig as { functionCallingConfig?: unknown }).functionCallingConfig,
-    ).toEqual({
-      mode: "AUTO",
-    });
     expect(result.api).toBe("google-generative-ai");
     expect(result.provider).toBe("google");
     expect(result.responseId).toBe("resp_1");
@@ -1532,6 +1527,36 @@ describe("google transport stream", () => {
     expect(params.cachedContent).toBe("cachedContents/prebuilt-context");
   });
 
+  it("omits per-request system and tool settings when using cachedContent", () => {
+    const params = buildGoogleGenerativeAiParams(
+      buildGeminiModel(),
+      {
+        systemPrompt: "Follow policy.",
+        messages: [{ role: "user", content: "hello", timestamp: 0 }],
+        tools: [
+          {
+            name: "lookup",
+            description: "Look up a value",
+            parameters: {
+              type: "object",
+              properties: { q: { type: "string" } },
+              required: ["q"],
+            },
+          },
+        ],
+      } as never,
+      {
+        cachedContent: " cachedContents/prebuilt-context ",
+        toolChoice: "auto",
+      },
+    );
+
+    expect(params.cachedContent).toBe("cachedContents/prebuilt-context");
+    expect(params.systemInstruction).toBeUndefined();
+    expect(params.tools).toBeUndefined();
+    expect(params.toolConfig).toBeUndefined();
+  });
+
   it("uses a non-empty text placeholder for empty user text", () => {
     const params = buildGoogleGenerativeAiParams(buildGeminiModel(), {
       messages: [
diff --git a/extensions/google/transport-stream.ts b/extensions/google/transport-stream.ts
index e3641cb3521d..f06bf5d97c74 100644
--- a/extensions/google/transport-stream.ts
+++ b/extensions/google/transport-stream.ts
@@ -202,9 +202,7 @@ function hasGeminiThoughtSignatureTruncationFootprint(value: string): boolean {
   );
 }
 
-function sanitizeGeminiThoughtSignature(
-  thoughtSignature: string | undefined,
-): string | undefined {
+function sanitizeGeminiThoughtSignature(thoughtSignature: string | undefined): string | undefined {
   if (typeof thoughtSignature !== "string") {
     return undefined;
   }
@@ -552,9 +550,7 @@ function convertGoogleMessages(model: GoogleTransportModel, context: Context) {
             : undefined;
           parts.push({
             text: sanitizeTransportPayloadText(block.text),
-            ...(sanitizedTextSignature
-              ? { thoughtSignature: sanitizedTextSignature }
-              : {}),
+            ...(sanitizedTextSignature ? { thoughtSignature: sanitizedTextSignature } : {}),
           });
           continue;
         }
@@ -710,13 +706,15 @@ export function buildGoogleGenerativeAiParams(
   const params: GoogleGenerateContentRequest = {
     contents: convertGoogleMessages(model, context),
   };
-  if (typeof options?.cachedContent === "string" && options.cachedContent.trim()) {
-    params.cachedContent = options.cachedContent.trim();
+  const cachedContent =
+    typeof options?.cachedContent === "string" ? options.cachedContent.trim() : "";
+  if (cachedContent) {
+    params.cachedContent = cachedContent;
   }
   if (Object.keys(generationConfig).length > 0) {
     params.generationConfig = generationConfig;
   }
-  if (context.systemPrompt) {
+  if (!cachedContent && context.systemPrompt) {
     params.systemInstruction = {
       parts: [
         {
@@ -725,7 +723,7 @@ export function buildGoogleGenerativeAiParams(
       ],
     };
   }
-  if (context.tools?.length) {
+  if (!cachedContent && context.tools?.length) {
     params.tools = convertGoogleTools(context.tools);
     const toolChoice = mapToolChoice(options?.toolChoice);
     if (toolChoice) {