diff --git a/src/auto-reply/reply/get-reply-directives.ts b/src/auto-reply/reply/get-reply-directives.ts
index f421ed92eae..ba1b1c0656e 100644
--- a/src/auto-reply/reply/get-reply-directives.ts
+++ b/src/auto-reply/reply/get-reply-directives.ts
@@ -390,10 +390,14 @@ export async function resolveReplyDirectives(params: {
   model = modelState.model;
 
   // When neither directive nor session set reasoning, default to model capability (e.g. OpenRouter with reasoning: true).
+  // Skip auto-enabling when thinking is already active — the model's internal
+  // thinking blocks would otherwise be formatted and delivered as visible
+  // "Reasoning:" messages, leaking internal content to the user.
   const reasoningExplicitlySet =
     directives.reasoningLevel !== undefined ||
     (sessionEntry?.reasoningLevel !== undefined && sessionEntry?.reasoningLevel !== null);
-  if (!reasoningExplicitlySet && resolvedReasoningLevel === "off") {
+  const thinkingActive = resolvedThinkLevel !== undefined && resolvedThinkLevel !== "off";
+  if (!reasoningExplicitlySet && resolvedReasoningLevel === "off" && !thinkingActive) {
     resolvedReasoningLevel = await modelState.resolveDefaultReasoningLevel();
   }