diff --git a/src/agents/pi-embedded-runner-extraparams.test.ts b/src/agents/pi-embedded-runner-extraparams.test.ts
index 46e72ed89ec..985d90e0db6 100644
--- a/src/agents/pi-embedded-runner-extraparams.test.ts
+++ b/src/agents/pi-embedded-runner-extraparams.test.ts
@@ -317,6 +317,38 @@ describe("applyExtraParamsToAgent", () => {
     expect(payloads[0]).toEqual({ reasoning: { max_tokens: 256 } });
   });
 
+  it("does not inject reasoning.effort for x-ai/grok models on OpenRouter (#32039)", () => {
+    const payloads: Record<string, unknown>[] = [];
+    const baseStreamFn: StreamFn = (_model, _context, options) => {
+      const payload: Record<string, unknown> = {};
+      options?.onPayload?.(payload);
+      payloads.push(payload);
+      return {} as ReturnType<StreamFn>;
+    };
+    const agent = { streamFn: baseStreamFn };
+
+    applyExtraParamsToAgent(
+      agent,
+      undefined,
+      "openrouter",
+      "x-ai/grok-4.1-fast",
+      undefined,
+      "medium",
+    );
+
+    const model = {
+      api: "openai-completions",
+      provider: "openrouter",
+      id: "x-ai/grok-4.1-fast",
+    } as Model<"openai-completions">;
+    const context: Context = { messages: [] };
+    void agent.streamFn?.(model, context, {});
+
+    expect(payloads).toHaveLength(1);
+    expect(payloads[0]).not.toHaveProperty("reasoning");
+    expect(payloads[0]).not.toHaveProperty("reasoning_effort");
+  });
+
   it("normalizes thinking=off to null for SiliconFlow Pro models", () => {
     const payloads: Record<string, unknown>[] = [];
     const baseStreamFn: StreamFn = (_model, _context, options) => {
diff --git a/src/agents/pi-embedded-runner/extra-params.ts b/src/agents/pi-embedded-runner/extra-params.ts
index 75dc4e85324..4258f758dea 100644
--- a/src/agents/pi-embedded-runner/extra-params.ts
+++ b/src/agents/pi-embedded-runner/extra-params.ts
@@ -620,6 +620,15 @@ function createOpenRouterWrapper(
   };
 }
 
+/**
+ * Models on OpenRouter that do not support the `reasoning.effort` parameter.
+ * Injecting it causes "Invalid arguments passed to the model" errors.
+ */
+function isOpenRouterReasoningUnsupported(modelId: string): boolean {
+  const id = modelId.toLowerCase();
+  return id.startsWith("x-ai/");
+}
+
 function isGemini31Model(modelId: string): boolean {
   const normalized = modelId.toLowerCase();
   return normalized.includes("gemini-3.1-pro") || normalized.includes("gemini-3.1-flash");
@@ -807,7 +816,13 @@ export function applyExtraParamsToAgent(
     // which would cause a 400 on models where reasoning is mandatory.
     // Users who need reasoning control should target a specific model ID.
     // See: openclaw/openclaw#24851
-    const openRouterThinkingLevel = modelId === "auto" ? undefined : thinkingLevel;
+    //
+    // x-ai/grok models do not support OpenRouter's reasoning.effort parameter
+    // and reject payloads containing it with "Invalid arguments passed to the
+    // model." Skip reasoning injection for these models.
+    // See: openclaw/openclaw#32039
+    const skipReasoningInjection = modelId === "auto" || isOpenRouterReasoningUnsupported(modelId);
+    const openRouterThinkingLevel = skipReasoningInjection ? undefined : thinkingLevel;
     agent.streamFn = createOpenRouterWrapper(agent.streamFn, openRouterThinkingLevel);
     agent.streamFn = createOpenRouterSystemCacheWrapper(agent.streamFn);
   }