diff --git a/api/core/mcp/client/streamable_client.py b/api/core/mcp/client/streamable_client.py
index f81e7cead8..5c3cd0d8f8 100644
--- a/api/core/mcp/client/streamable_client.py
+++ b/api/core/mcp/client/streamable_client.py
@@ -313,17 +313,20 @@ class StreamableHTTPTransport:
             if is_initialization:
                 self._maybe_extract_session_id_from_response(response)
 
-            content_type = cast(str, response.headers.get(CONTENT_TYPE, "").lower())
+            # Per https://modelcontextprotocol.io/specification/2025-06-18/basic#notifications:
+            # The server MUST NOT send a response to notifications.
+            if isinstance(message.root, JSONRPCRequest):
+                content_type = cast(str, response.headers.get(CONTENT_TYPE, "").lower())
 
-            if content_type.startswith(JSON):
-                self._handle_json_response(response, ctx.server_to_client_queue)
-            elif content_type.startswith(SSE):
-                self._handle_sse_response(response, ctx)
-            else:
-                self._handle_unexpected_content_type(
-                    content_type,
-                    ctx.server_to_client_queue,
-                )
+                if content_type.startswith(JSON):
+                    self._handle_json_response(response, ctx.server_to_client_queue)
+                elif content_type.startswith(SSE):
+                    self._handle_sse_response(response, ctx)
+                else:
+                    self._handle_unexpected_content_type(
+                        content_type,
+                        ctx.server_to_client_queue,
+                    )
 
     def _handle_json_response(
         self,