diff --git a/open-sse/executors/antigravity.ts b/open-sse/executors/antigravity.ts
index 0fdb0f9a8e..b8dc191b7b 100644
--- a/open-sse/executors/antigravity.ts
+++ b/open-sse/executors/antigravity.ts
@@ -15,6 +15,10 @@ import { persistCreditBalance, getAllPersistedCreditBalances } from "@/lib/db/cr
 import { obfuscateSensitiveWords } from "../services/antigravityObfuscation.ts";
 import { resolveAntigravityVersion } from "../services/antigravityVersion.ts";
 import { resolveAntigravityModelId } from "../config/antigravityModelAliases.ts";
+import {
+  shouldStripCloudCodeThinking,
+  stripCloudCodeThinkingConfig,
+} from "../services/cloudCodeThinking.ts";
 
 const MAX_RETRY_AFTER_MS = 60_000;
 const LONG_RETRY_THRESHOLD_MS = 60_000;
@@ -166,9 +170,15 @@ export class AntigravityExecutor extends BaseExecutor {
       return resp as unknown as never;
     }
 
+    const upstreamModel = cleanModelName(model);
+    const baseBody = body && typeof body === "object" ? body : {};
+    const normalizedBody = shouldStripCloudCodeThinking(this.provider, upstreamModel)
+      ? stripCloudCodeThinkingConfig(baseBody)
+      : baseBody;
+
     // Fix contents for Claude models via Antigravity
     const normalizedContents =
-      body.request?.contents?.map((c) => {
+      normalizedBody.request?.contents?.map((c) => {
         let role = c.role;
         // functionResponse must be role "user" for Claude models
         if (c.parts?.some((p) => p.functionResponse)) {
@@ -203,18 +213,16 @@ export class AntigravityExecutor extends BaseExecutor {
     }
 
     const transformedRequest = {
-      ...body.request,
+      ...normalizedBody.request,
       ...(contents.length > 0 && { contents }),
-      sessionId: body.request?.sessionId || this.generateSessionId(),
+      sessionId: normalizedBody.request?.sessionId || this.generateSessionId(),
       safetySettings: undefined,
       toolConfig:
-        body.request?.tools?.length > 0
+        normalizedBody.request?.tools?.length > 0
           ? { functionCallingConfig: { mode: "VALIDATED" } }
-          : body.request?.toolConfig,
+          : normalizedBody.request?.toolConfig,
     };
 
-    const upstreamModel = cleanModelName(model);
-
     // Obfuscate sensitive client names in user content (e.g. "OpenCode", "Cursor")
     const requestContents = transformedRequest.contents;
     if (Array.isArray(requestContents)) {
@@ -230,7 +238,7 @@ export class AntigravityExecutor extends BaseExecutor {
     }
 
     return {
-      ...body,
+      ...normalizedBody,
       project: projectId,
       model: upstreamModel,
       userAgent: "antigravity",
diff --git a/open-sse/executors/gemini-cli.ts b/open-sse/executors/gemini-cli.ts
index 7031dc9d12..e2560a1e07 100644
--- a/open-sse/executors/gemini-cli.ts
+++ b/open-sse/executors/gemini-cli.ts
@@ -3,6 +3,10 @@ import { PROVIDERS, OAUTH_ENDPOINTS } from "../config/constants.ts";
 import { geminiCLIUserAgent, googApiClientHeader } from "../services/antigravityHeaders.ts";
 import { scrubProxyAndFingerprintHeaders } from "../services/antigravityHeaderScrub.ts";
 import { obfuscateSensitiveWords } from "../services/antigravityObfuscation.ts";
+import {
+  shouldStripCloudCodeThinking,
+  stripCloudCodeThinkingConfig,
+} from "../services/cloudCodeThinking.ts";
 
 const LOAD_CODE_ASSIST_URL = "https://cloudcode-pa.googleapis.com/v1internal:loadCodeAssist";
 const ONBOARD_USER_URL = "https://cloudcode-pa.googleapis.com/v1internal:onboardUser";
@@ -276,16 +280,24 @@ export class GeminiCLIExecutor extends BaseExecutor {
 
   async transformRequest(model, body, stream, credentials) {
     this._currentModel = normalizeGeminiModel(model);
+    const normalizedBody =
+      shouldStripCloudCodeThinking(this.provider, this._currentModel) &&
+      body &&
+      typeof body === "object"
+        ? stripCloudCodeThinkingConfig(body)
+        : body;
 
     // Refresh the project ID via loadCodeAssist (cached for 30s).
-    if (body && typeof body === "object" && body.request && credentials.accessToken) {
-      const freshProject = await this.refreshProject(credentials.accessToken);
-      if (freshProject) {
-        body.project = freshProject;
+    if (normalizedBody && typeof normalizedBody === "object" && normalizedBody.request) {
+      if (credentials.accessToken) {
+        const freshProject = await this.refreshProject(credentials.accessToken);
+        if (freshProject) {
+          normalizedBody.project = freshProject;
+        }
       }
 
       // Obfuscate sensitive client names in user content
-      const contents = body.request?.contents;
+      const contents = normalizedBody.request?.contents;
       if (Array.isArray(contents)) {
         for (const msg of contents) {
           if (Array.isArray(msg.parts)) {
@@ -298,7 +310,7 @@ export class GeminiCLIExecutor extends BaseExecutor {
         }
       }
     }
-    return body;
+    return normalizedBody;
   }
 
   async refreshCredentials(credentials, log) {
diff --git a/open-sse/services/AGENTS.md b/open-sse/services/AGENTS.md
index 9cfe947ac6..b5af3cbdd1 100644
--- a/open-sse/services/AGENTS.md
+++ b/open-sse/services/AGENTS.md
@@ -30,6 +30,7 @@
 - **`intentClassifier.ts`** — Classifies request intent (chat, embedding, image, video, etc.) for intelligent routing.
 - **`taskAwareRouter.ts`** — Routes based on task characteristics (reasoning-heavy → o1, code-gen → Cursor, long-context → Claude).
 - **`thinkingBudget.ts`** — Allocates thinking tokens for o1/o3 models; enforces per-request budget.
+  Provider-specific Cloud Code compatibility stripping belongs in executors, not in this service.
 - **`contextManager.ts`** — Injects routing context (system prompts, memory) into requests.
 
 ### Model Lifecycle & Fallback
diff --git a/open-sse/services/cloudCodeThinking.ts b/open-sse/services/cloudCodeThinking.ts
new file mode 100644
index 0000000000..8a44a8973e
--- /dev/null
+++ b/open-sse/services/cloudCodeThinking.ts
@@ -0,0 +1,44 @@
+import { supportsReasoning } from "./modelCapabilities.ts";
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return !!value && typeof value === "object" && !Array.isArray(value);
+}
+
+function stripGeminiThinkingConfig(value: unknown): unknown {
+  if (!isRecord(value)) return value;
+  if (!("thinkingConfig" in value) && !("thinking_config" in value)) return value;
+
+  const next = { ...value };
+  delete next.thinkingConfig;
+  delete next.thinking_config;
+  return next;
+}
+
+export function shouldStripCloudCodeThinking(provider: string, model: string): boolean {
+  if (!provider || !model) return false;
+  return !supportsReasoning(`${provider}/${model}`);
+}
+
+export function stripCloudCodeThinkingConfig(
+  body: Record<string, unknown>
+): Record<string, unknown> {
+  const next = { ...body };
+
+  delete next.reasoning_effort;
+  delete next.reasoning;
+  delete next.thinking;
+
+  if ("generationConfig" in next) {
+    next.generationConfig = stripGeminiThinkingConfig(next.generationConfig);
+  }
+
+  if (isRecord(next.request)) {
+    const request = { ...next.request };
+    if ("generationConfig" in request) {
+      request.generationConfig = stripGeminiThinkingConfig(request.generationConfig);
+    }
+    next.request = request;
+  }
+
+  return next;
+}
diff --git a/open-sse/services/thinkingBudget.ts b/open-sse/services/thinkingBudget.ts
index ae03ae76db..d1004052de 100644
--- a/open-sse/services/thinkingBudget.ts
+++ b/open-sse/services/thinkingBudget.ts
@@ -157,10 +157,9 @@ export function applyThinkingBudget(body, config = null) {
   if (!body || typeof body !== "object") return body;
 
   // Early exit: strip ALL reasoning/thinking params for models that don't support them.
-  // Sending thinking params to unsupported models (e.g. AG claude-sonnet-4-6) causes 400 errors.
+  // Provider-specific Cloud Code restrictions should be handled at the executor boundary.
   const modelStr = typeof body.model === "string" ? body.model : "";
-  const isClaude = modelStr.toLowerCase().includes("claude");
-  if (modelStr && (!supportsReasoning(modelStr) || (!isClaude && modelStr.includes("gemini")))) {
+  if (modelStr && !supportsReasoning(modelStr)) {
     return stripThinkingConfig(body);
   }
 
diff --git a/tests/unit/executor-antigravity.test.ts b/tests/unit/executor-antigravity.test.ts
index 3fa9eec55c..eeeffcbedd 100644
--- a/tests/unit/executor-antigravity.test.ts
+++ b/tests/unit/executor-antigravity.test.ts
@@ -88,6 +88,63 @@ test("AntigravityExecutor.transformRequest normalizes model, project and content
   assert.equal(result.request.contents[1].role, "user");
 });
 
+test("AntigravityExecutor.transformRequest strips thinking config for Cloud Code models that do not support reasoning", async () => {
+  const executor = new AntigravityExecutor();
+  const body = {
+    reasoning_effort: "high",
+    request: {
+      generationConfig: {
+        thinkingConfig: {
+          thinkingBudget: 8192,
+          includeThoughts: true,
+        },
+      },
+      contents: [{ role: "user", parts: [{ text: "Hello" }] }],
+    },
+  };
+
+  const result = await executor.transformRequest("antigravity/claude-sonnet-4-6", body, true, {
+    projectId: "project-1",
+  });
+
+  assert.equal(result.reasoning_effort, undefined);
+  assert.equal(result.request.generationConfig.thinkingConfig, undefined);
+});
+
+test("AntigravityExecutor.transformRequest preserves thinking config for supported Gemini models", async () => {
+  const executor = new AntigravityExecutor();
+  const body = {
+    request: {
+      generationConfig: {
+        thinkingConfig: {
+          thinkingBudget: 8192,
+          includeThoughts: true,
+        },
+      },
+      contents: [{ role: "user", parts: [{ text: "Hello" }] }],
+    },
+  };
+
+  const result = await executor.transformRequest("antigravity/gemini-3.1-pro-high", body, true, {
+    projectId: "project-1",
+  });
+
+  assert.equal(result.request.generationConfig.thinkingConfig.thinkingBudget, 8192);
+  assert.equal(result.request.generationConfig.thinkingConfig.includeThoughts, true);
+});
+
+test("AntigravityExecutor.transformRequest tolerates a missing body when projectId is present", async () => {
+  const executor = new AntigravityExecutor();
+
+  const result = await executor.transformRequest("antigravity/gemini-3.1-pro", null, true, {
+    projectId: "project-1",
+  });
+
+  assert.equal(result.project, "project-1");
+  assert.equal(result.model, "gemini-3.1-pro-low");
+  assert.ok(result.request.sessionId);
+});
+
 test("AntigravityExecutor.transformRequest returns a structured error response when projectId is missing", async () => {
   const executor = new AntigravityExecutor();
   const result = await executor.transformRequest(
diff --git a/tests/unit/executor-gemini-cli.test.ts b/tests/unit/executor-gemini-cli.test.ts
index ba0d7253a3..fb28a10ac7 100644
--- a/tests/unit/executor-gemini-cli.test.ts
+++ b/tests/unit/executor-gemini-cli.test.ts
@@ -56,6 +56,42 @@ test("GeminiCLIExecutor.refreshProject caches loadCodeAssist lookups and transfo
   }
 });
 
+test("GeminiCLIExecutor.transformRequest preserves thinking config for supported Gemini models", async () => {
+  const executor = new GeminiCLIExecutor();
+  const originalFetch = globalThis.fetch;
+
+  globalThis.fetch = async () =>
+    new Response(JSON.stringify({ cloudaicompanionProject: "fresh-project-id" }), {
+      status: 200,
+      headers: { "Content-Type": "application/json" },
+    });
+
+  try {
+    const transformed = await executor.transformRequest(
+      "models/gemini-3.1-pro-preview",
+      {
+        request: {
+          contents: [{ role: "user", parts: [{ text: "Hello" }] }],
+          generationConfig: {
+            thinkingConfig: {
+              thinkingBudget: 8192,
+              includeThoughts: true,
+            },
+          },
+        },
+      },
+      true,
+      { accessToken: "access-token-1" }
+    );
+
+    assert.equal(transformed.project, "fresh-project-id");
+    assert.equal(transformed.request.generationConfig.thinkingConfig.thinkingBudget, 8192);
+    assert.equal(transformed.request.generationConfig.thinkingConfig.includeThoughts, true);
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+});
+
 test("GeminiCLIExecutor.refreshProject returns null on failed loadCodeAssist responses", async () => {
   const executor = new GeminiCLIExecutor();
   const originalFetch = globalThis.fetch;
diff --git a/tests/unit/thinking-budget.test.ts b/tests/unit/thinking-budget.test.ts
index ee7cdcfa3d..5242f42f8d 100644
--- a/tests/unit/thinking-budget.test.ts
+++ b/tests/unit/thinking-budget.test.ts
@@ -42,6 +42,18 @@ test("PASSTHROUGH: body unchanged", () => {
   setThinkingBudgetConfig(DEFAULT_THINKING_CONFIG);
 });
 
+test("PASSTHROUGH: keeps reasoning_effort for OpenAI-compatible Gemini routes", () => {
+  setThinkingBudgetConfig({ mode: ThinkingMode.PASSTHROUGH });
+  const body = {
+    model: "openai-compatible-sp-google/gemini-3.1-pro-preview",
+    messages: [{ role: "user", content: "hello" }],
+    reasoning_effort: "high",
+  };
+  const result = applyThinkingBudget(body);
+  assert.equal(result.reasoning_effort, "high");
+  setThinkingBudgetConfig(DEFAULT_THINKING_CONFIG);
+});
+
 // ─── AUTO Mode ──────────────────────────────────────────────────────────────
 
 test("AUTO: strips Claude thinking config", () => {