diff --git a/backend/internal/handler/openai_gateway_handler.go b/backend/internal/handler/openai_gateway_handler.go
index b787d0f976..ea60b26692 100644
--- a/backend/internal/handler/openai_gateway_handler.go
+++ b/backend/internal/handler/openai_gateway_handler.go
@@ -2696,7 +2696,11 @@ func (h *OpenAIGatewayHandler) ensureForwardErrorResponse(c *gin.Context, stream
 		imageKeepalivePaddingOnly = adjustedSize < 0
 		imageKeepaliveResponseWritten = adjustedSize >= 0
 	}
-	if service.IsResponseCommitted(c) || (!compactKeepaliveCommitted && imageKeepaliveResponseWritten) {
+	compactKeepaliveHasMeaningfulOutput := compactKeepaliveCommitted && service.OpenAICompactKeepaliveAdjustedWrittenSize(c) > 0
+	// Compact keepalive may have committed 200 headers without writing a
+	// semantic SSE event. In that case the Responses stream still needs its
+	// protocol-correct terminal response.failed event.
+	if (service.IsResponseCommitted(c) && (!compactKeepaliveCommitted || compactKeepaliveHasMeaningfulOutput)) || (!compactKeepaliveCommitted && imageKeepaliveResponseWritten) {
 		return false
 	}
 	if c.Writer.Written() && !imageKeepalivePaddingOnly {
diff --git a/backend/internal/handler/openai_gateway_handler_test.go b/backend/internal/handler/openai_gateway_handler_test.go
index 543cda1e55..82e530cbe4 100644
--- a/backend/internal/handler/openai_gateway_handler_test.go
+++ b/backend/internal/handler/openai_gateway_handler_test.go
@@ -334,6 +334,26 @@ func TestOpenAIEnsureForwardErrorResponse_AfterDeltaAppendsSingleValidResponseFa
 	require.Equal(t, 1, errorEvents)
 }
 
+func TestOpenAIEnsureForwardErrorResponse_CompactKeepaliveOnlyWritesResponseFailed(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest(http.MethodPost, EndpointResponses, nil)
+	service.MarkOpenAICompactClientStream(c)
+
+	stop := service.StartOpenAICompactSSEKeepalive(c, 5*time.Millisecond)
+	defer stop()
+	before := service.OpenAICompactKeepaliveAdjustedWrittenSize(c)
+	require.Eventually(t, c.Writer.Written, time.Second, time.Millisecond)
+	require.Equal(t, before, service.OpenAICompactKeepaliveAdjustedWrittenSize(c))
+
+	h := &OpenAIGatewayHandler{}
+	require.True(t, h.ensureForwardErrorResponse(c, false))
+	require.Equal(t, http.StatusOK, w.Code)
+	require.Contains(t, w.Body.String(), "event: response.failed\n")
+	require.NotContains(t, w.Body.String(), "event: error\n")
+}
+
 func TestOpenAIEnsureForwardErrorResponse_ImageJSONKeepaliveWritesSingleJSONFallback(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	w := httptest.NewRecorder()