diff --git a/src/agents/models-config.providers.ts b/src/agents/models-config.providers.ts
index 3662ce9a3..4f921b6dd 100644
--- a/src/agents/models-config.providers.ts
+++ b/src/agents/models-config.providers.ts
@@ -685,6 +685,12 @@ function buildOpenrouterProvider(): ProviderConfig {
       {
         id: OPENROUTER_DEFAULT_MODEL_ID,
         name: "OpenRouter Auto",
+        // reasoning: false here is a catalog default only; it does NOT cause
+        // `reasoning.effort: "none"` to be sent for the "auto" routing model.
+        // applyExtraParamsToAgent skips the reasoning effort injection for
+        // model id "auto" because it dynamically routes to any OpenRouter model
+        // (including ones where reasoning is mandatory and cannot be disabled).
+        // See: openclaw/openclaw#24851
         reasoning: false,
         input: ["text", "image"],
         cost: OPENROUTER_DEFAULT_COST,
diff --git a/src/agents/pi-embedded-runner/extra-params.ts b/src/agents/pi-embedded-runner/extra-params.ts
index 66b077af2..0d88bdf08 100644
--- a/src/agents/pi-embedded-runner/extra-params.ts
+++ b/src/agents/pi-embedded-runner/extra-params.ts
@@ -546,7 +546,14 @@ export function applyExtraParamsToAgent(
 
   if (provider === "openrouter") {
     log.debug(`applying OpenRouter app attribution headers for ${provider}/${modelId}`);
-    agent.streamFn = createOpenRouterWrapper(agent.streamFn, thinkingLevel);
+    // "auto" is a dynamic routing model — we don't know which underlying model
+    // OpenRouter will select, and it may be a reasoning-required endpoint.
+    // Omit the thinkingLevel so we never inject `reasoning.effort: "none"`,
+    // 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;
+    agent.streamFn = createOpenRouterWrapper(agent.streamFn, openRouterThinkingLevel);
     agent.streamFn = createOpenRouterSystemCacheWrapper(agent.streamFn);
   }