diff --git a/src/adapters/google.ts b/src/adapters/google.ts
index c9d7aedfc..be861d4ce 100644
--- a/src/adapters/google.ts
+++ b/src/adapters/google.ts
@@ -12,7 +12,7 @@ import type {
   OcxToolCall,
   OcxUsage,
 } from "../types";
-import { isAllowedToolChoice, namespacedToolName, toolAllowedByChoice } from "../types";
+import { isAllowedToolChoice, namespacedToolName, resolveToolChoiceWireName, toolAllowedByChoice } from "../types";
 import { contentPartsToText, parseDataUrl } from "./image";
 import { getVertexAccessToken } from "../lib/gcp-adc";
 import { fetchAntigravityWithRetry, fetchVertexWithRetry } from "./google-http";
@@ -232,6 +232,28 @@ function toolsToGeminiFormat(parsed: OcxParsedRequest): unknown[] | undefined {
   }];
 }
 
+/**
+ * Client tool_choice enforcement on the wire. The catalog nudge states the same contract in
+ * prose, but without functionCallingConfig the model is free to ignore it. "auto" stays absent
+ * so the common case is byte-identical. The allowedTools variant already filters the
+ * declarations in toolsToGeminiFormat; only its "required" half needs a wire mode.
+ */
+function toolChoiceToGeminiToolConfig(parsed: OcxParsedRequest): Record<string, unknown> | undefined {
+  const choice = parsed.options.toolChoice;
+  if (!choice || choice === "auto") return undefined;
+  if (choice === "none") return { functionCallingConfig: { mode: "NONE" } };
+  if (choice === "required") return { functionCallingConfig: { mode: "ANY" } };
+  if (isAllowedToolChoice(choice)) {
+    return choice.mode === "required" ? { functionCallingConfig: { mode: "ANY" } } : undefined;
+  }
+  return {
+    functionCallingConfig: {
+      mode: "ANY",
+      allowedFunctionNames: [resolveToolChoiceWireName(parsed.context.tools, choice.name)],
+    },
+  };
+}
+
 function usageFromGemini(usage: Record<string, number> | undefined): OcxUsage | undefined {
   if (!usage) return undefined;
   return {
@@ -307,6 +329,10 @@ export function createGoogleAdapter(provider: OcxProviderConfig): ProviderAdapte
       const body: Record<string, unknown> = { contents };
       if (systemInstruction) body.systemInstruction = systemInstruction;
       if (tools) body.tools = tools;
+      // Only meaningful with declarations on the wire: mode ANY with an empty
+      // catalog is a guaranteed upstream 400.
+      const toolConfig = tools ? toolChoiceToGeminiToolConfig(parsed) : undefined;
+      if (toolConfig) body.toolConfig = toolConfig;
 
       const generationConfig: Record<string, unknown> = {};
       if (parsed.options.maxOutputTokens) generationConfig.maxOutputTokens = parsed.options.maxOutputTokens;
@@ -358,6 +384,12 @@ export function createGoogleAdapter(provider: OcxProviderConfig): ProviderAdapte
         const draftRequest: Record<string, unknown> = { ...body, sessionId };
         // Claude-on-Antigravity forces VALIDATED function calling (the real client always sets it).
         if (/claude/i.test(wireModelId)) {
+          // VALIDATED would defeat a client's tool_choice "none": honor it by dropping the
+          // declarations instead, the wire shape of a tool-less Claude turn.
+          if (parsed.options.toolChoice === "none") {
+            delete draftRequest.tools;
+            delete draftRequest.toolConfig;
+          }
           const existing = (draftRequest.toolConfig ?? {}) as Record<string, unknown>;
           const fcc = (existing.functionCallingConfig ?? {}) as Record<string, unknown>;
           draftRequest.toolConfig = { ...existing, functionCallingConfig: { ...fcc, mode: "VALIDATED" } };
diff --git a/tests/google-adapter.test.ts b/tests/google-adapter.test.ts
index 4eecd1d48..467cf19c3 100644
--- a/tests/google-adapter.test.ts
+++ b/tests/google-adapter.test.ts
@@ -189,3 +189,92 @@ describe("google adapter — tool-call ids on the wire", () => {
     expect(fc).toBe("call_xyz");
   });
 });
+
+describe("google adapter — tool_choice on the wire", () => {
+  const TOOLS = [
+    { name: "get_weather", parameters: { type: "object", properties: {} } },
+    { name: "shot", namespace: "mcp__chrome", parameters: { type: "object", properties: {} } },
+  ];
+
+  function parsedWithChoice(toolChoice: unknown, tools: unknown[] | null = TOOLS): OcxParsedRequest {
+    return {
+      modelId: "gemini-3-pro",
+      stream: false,
+      options: toolChoice === undefined ? {} : { toolChoice },
+      context: { messages: [{ role: "user", content: "hi" }], tools: tools ?? undefined },
+    } as unknown as OcxParsedRequest;
+  }
+
+  test('"none" and "required" map to NONE and ANY', async () => {
+    expect((await geminiBody(parsedWithChoice("none"))).toolConfig)
+      .toEqual({ functionCallingConfig: { mode: "NONE" } });
+    expect((await geminiBody(parsedWithChoice("required"))).toolConfig)
+      .toEqual({ functionCallingConfig: { mode: "ANY" } });
+  });
+
+  test("a forced tool maps to ANY with its wire name allowed", async () => {
+    expect((await geminiBody(parsedWithChoice({ name: "get_weather" }))).toolConfig)
+      .toEqual({ functionCallingConfig: { mode: "ANY", allowedFunctionNames: ["get_weather"] } });
+    // Dotted alias resolves to the namespaced declaration name.
+    expect((await geminiBody(parsedWithChoice({ name: "mcp__chrome.shot" }))).toolConfig)
+      .toEqual({ functionCallingConfig: { mode: "ANY", allowedFunctionNames: ["mcp__chrome__shot"] } });
+  });
+
+  test('"auto", absent, and allowedTools+auto stay byte-identical (no toolConfig)', async () => {
+    expect((await geminiBody(parsedWithChoice("auto"))).toolConfig).toBeUndefined();
+    expect((await geminiBody(parsedWithChoice(undefined))).toolConfig).toBeUndefined();
+    expect((await geminiBody(parsedWithChoice({ allowedTools: ["get_weather"], mode: "auto" }))).toolConfig).toBeUndefined();
+  });
+
+  test("allowedTools with mode required keeps the filtered catalog and adds ANY", async () => {
+    const body = await geminiBody(parsedWithChoice({ allowedTools: ["get_weather"], mode: "required" }));
+    const declared = (body.tools as { functionDeclarations: { name: string }[] }[])[0].functionDeclarations.map(d => d.name);
+    expect(declared).toEqual(["get_weather"]);
+    expect(body.toolConfig).toEqual({ functionCallingConfig: { mode: "ANY" } });
+  });
+
+  test("no declared tools means no toolConfig even with a choice", async () => {
+    expect((await geminiBody(parsedWithChoice("none", null))).toolConfig).toBeUndefined();
+    expect((await geminiBody(parsedWithChoice({ name: "get_weather" }, []))).toolConfig).toBeUndefined();
+  });
+
+  test('claude-on-antigravity honors "none" by dropping the declarations', async () => {
+    const ccaProvider = {
+      adapter: "google",
+      googleMode: "cloud-code-assist",
+      baseUrl: "https://daily-cloudcode-pa.googleapis.com",
+      apiKey: "key",
+      project: "proj-123",
+    };
+    const claudeParsed = parsedWithChoice("none");
+    (claudeParsed as unknown as { modelId: string }).modelId = "claude-opus-4.8";
+    const claudeRequest = JSON.parse((await createGoogleAdapter(ccaProvider).buildRequest(claudeParsed)).body).request as Record<string, unknown>;
+    // VALIDATED would defeat NONE, so the declarations go instead; the config matches a tool-less turn.
+    expect(claudeRequest.tools).toBeUndefined();
+    expect(claudeRequest.toolConfig).toEqual({ functionCallingConfig: { mode: "VALIDATED" } });
+
+    // Gemini on the same route has no VALIDATED override, so NONE rides with the catalog intact.
+    const geminiParsed = parsedWithChoice("none");
+    const geminiRequest = JSON.parse((await createGoogleAdapter(ccaProvider).buildRequest(geminiParsed)).body).request as Record<string, unknown>;
+    const declared = (geminiRequest.tools as { functionDeclarations: { name: string }[] }[])[0].functionDeclarations.map(d => d.name);
+    expect(declared).toEqual(["get_weather", "mcp__chrome__shot"]);
+    expect(geminiRequest.toolConfig).toEqual({ functionCallingConfig: { mode: "NONE" } });
+  });
+
+  test("claude-on-antigravity keeps VALIDATED mode over a client choice, allowed names survive", async () => {
+    const ccaProvider = {
+      adapter: "google",
+      googleMode: "cloud-code-assist",
+      baseUrl: "https://daily-cloudcode-pa.googleapis.com",
+      apiKey: "key",
+      project: "proj-123",
+    };
+    const parsed = parsedWithChoice({ name: "get_weather" });
+    (parsed as unknown as { modelId: string }).modelId = "claude-opus-4.8";
+    const { body } = await createGoogleAdapter(ccaProvider).buildRequest(parsed);
+    const request = JSON.parse(body).request as Record<string, unknown>;
+    expect(request.toolConfig).toEqual({
+      functionCallingConfig: { mode: "VALIDATED", allowedFunctionNames: ["get_weather"] },
+    });
+  });
+});