diff --git a/extensions/matrix/src/matrix/monitor/replies.ts b/extensions/matrix/src/matrix/monitor/replies.ts
index 643e95cd413..c86c7dde688 100644
--- a/extensions/matrix/src/matrix/monitor/replies.ts
+++ b/extensions/matrix/src/matrix/monitor/replies.ts
@@ -41,6 +41,11 @@ export async function deliverMatrixReplies(params: {
       params.runtime.error?.("matrix reply missing text/media");
       continue;
     }
+    // Skip pure reasoning messages so internal thinking traces are never delivered.
+    if (reply.text && isReasoningOnlyMessage(reply.text)) {
+      logVerbose("matrix reply is reasoning-only; skipping");
+      continue;
+    }
     const replyToIdRaw = reply.replyToId?.trim();
     const replyToId = params.threadId || params.replyToMode === "off" ? undefined : replyToIdRaw;
     const rawText = reply.text ?? "";
@@ -98,3 +103,22 @@ export async function deliverMatrixReplies(params: {
     }
   }
 }
+
+const REASONING_PREFIX = "Reasoning:\n";
+const THINKING_TAG_RE = /^\s*<\s*(?:think(?:ing)?|thought|antthinking)\b/i;
+
+/**
+ * Detect messages that contain only reasoning/thinking content and no user-facing answer.
+ * These are emitted by the agent when `includeReasoning` is active but should not
+ * be forwarded to channels that do not support a dedicated reasoning lane.
+ */
+function isReasoningOnlyMessage(text: string): boolean {
+  const trimmed = text.trim();
+  if (trimmed.startsWith(REASONING_PREFIX)) {
+    return true;
+  }
+  if (THINKING_TAG_RE.test(trimmed)) {
+    return true;
+  }
+  return false;
+}