diff --git a/internal/runtime/executor/codex_executor_stream.go b/internal/runtime/executor/codex_executor_stream.go
index 098311683..d6e622646 100644
--- a/internal/runtime/executor/codex_executor_stream.go
+++ b/internal/runtime/executor/codex_executor_stream.go
@@ -58,7 +58,11 @@ func (e *CodexExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth.Au
 	body, _ = sjson.DeleteBytes(body, "generate")
 	body, _ = sjson.DeleteBytes(body, "prompt_cache_retention")
 	body, _ = sjson.DeleteBytes(body, "safety_identifier")
+	reasoningSummaryDelivery := gjson.GetBytes(body, "stream_options.reasoning_summary_delivery")
 	body, _ = sjson.DeleteBytes(body, "stream_options")
+	if reasoningSummaryDelivery.Exists() {
+		body, _ = sjson.SetBytes(body, "stream_options.reasoning_summary_delivery", reasoningSummaryDelivery.Value())
+	}
 	body = helps.SetStringIfDifferent(body, "model", baseModel)
 	body = normalizeCodexInstructions(body)
 	if e.cfg == nil || e.cfg.DisableImageGeneration == config.DisableImageGenerationOff {
diff --git a/internal/runtime/executor/codex_executor_stream_output_test.go b/internal/runtime/executor/codex_executor_stream_output_test.go
index 19b38fb54..3d1fbcf51 100644
--- a/internal/runtime/executor/codex_executor_stream_output_test.go
+++ b/internal/runtime/executor/codex_executor_stream_output_test.go
@@ -288,6 +288,56 @@ func TestCodexExecutorExecuteStreamExplicitTerminalFailureIsNotSuccessful(t *tes
 	assertNotRequestScopedTestError(t, streamErr)
 }
 
+func TestCodexAutoExecutorHTTPFallbackForwardsSequentialCutoffReasoningSummaryDelivery(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, errRead := io.ReadAll(r.Body)
+		if errRead != nil {
+			t.Errorf("read request body: %v", errRead)
+			return
+		}
+		if gjson.GetBytes(body, "stream_options.include_usage").Exists() {
+			t.Errorf("unsupported stream option was forwarded: %s", body)
+		}
+
+		w.Header().Set("Content-Type", "text/event-stream")
+		if delivery := gjson.GetBytes(body, "stream_options.reasoning_summary_delivery").String(); delivery == "sequential_cutoff" {
+			_, _ = w.Write([]byte(`data: {"type":"response.reasoning_summary_text.done","item_id":"rs_1","summary_index":0,"text":"Checking"}` + "\n\n"))
+		} else {
+			_, _ = w.Write([]byte(`data: {"type":"response.reasoning_summary_text.delta","item_id":"rs_1","summary_index":0,"delta":"Checking"}` + "\n\n"))
+		}
+		_, _ = w.Write([]byte(`data: {"type":"response.completed","response":{"id":"resp_1","output":[],"usage":{"input_tokens":1,"output_tokens":1,"total_tokens":2}}}` + "\n\n"))
+	}))
+	defer server.Close()
+
+	executor := NewCodexAutoExecutor(&config.Config{})
+	auth := &cliproxyauth.Auth{Attributes: map[string]string{
+		"base_url": server.URL,
+		"api_key":  "test",
+	}}
+	result, err := executor.ExecuteStream(cliproxyexecutor.WithDownstreamWebsocket(context.Background()), auth, cliproxyexecutor.Request{
+		Model:   "gpt-5.6-sol",
+		Payload: []byte(`{"model":"gpt-5.6-sol","input":"hello","reasoning":{"summary":"detailed"},"stream_options":{"reasoning_summary_delivery":"sequential_cutoff","include_usage":true}}`),
+	}, cliproxyexecutor.Options{
+		SourceFormat:   sdktranslator.FromString("openai-response"),
+		ResponseFormat: sdktranslator.FromString("openai-response"),
+		Stream:         true,
+	})
+	if err != nil {
+		t.Fatalf("ExecuteStream error: %v", err)
+	}
+
+	var output bytes.Buffer
+	for chunk := range result.Chunks {
+		if chunk.Err != nil {
+			t.Fatalf("stream error: %v", chunk.Err)
+		}
+		output.Write(chunk.Payload)
+	}
+	if !strings.Contains(output.String(), `"type":"response.reasoning_summary_text.done"`) {
+		t.Fatalf("missing sequential-cutoff summary event; output=%s", output.String())
+	}
+}
+
 func TestCodexExecutorTransportFailureBeforeTerminalIsRequestScoped(t *testing.T) {
 	tests := []struct {
 		name   string