diff --git a/codex-rs/core/src/session_startup_prewarm.rs b/codex-rs/core/src/session_startup_prewarm.rs
index 13e0871e92a0..d620648179fb 100644
--- a/codex-rs/core/src/session_startup_prewarm.rs
+++ b/codex-rs/core/src/session_startup_prewarm.rs
@@ -172,6 +172,10 @@ impl SessionStartupPrewarmHandle {
 
 impl Session {
     pub(crate) async fn schedule_startup_prewarm(self: &Arc<Self>, base_instructions: String) {
+        if !self.services.model_client.responses_websocket_enabled() {
+            return;
+        }
+
         let session_telemetry = self.services.session_telemetry.clone();
         let websocket_connect_timeout = self.provider().await.websocket_connect_timeout();
         let started_at = Instant::now();