diff --git a/backend/internal/service/openai_gateway_passthrough.go b/backend/internal/service/openai_gateway_passthrough.go
index 44c9670a3e..030932befb 100644
--- a/backend/internal/service/openai_gateway_passthrough.go
+++ b/backend/internal/service/openai_gateway_passthrough.go
@@ -1160,6 +1160,7 @@ func (s *OpenAIGatewayService) handleStreamingResponsePassthrough(
 	sawDone := false
 	sawTerminalEvent := false
 	sawFailedEvent := false
+	semanticOutputSeen := false
 	failedMessage := ""
 	clientOutputStarted := false
 	upstreamRequestID := strings.TrimSpace(resp.Header.Get("x-request-id"))
@@ -1305,6 +1306,18 @@ func (s *OpenAIGatewayService) handleStreamingResponsePassthrough(
 				line = "data: " + string(sanitizedData)
 			}
 			lineStartsClientOutput = forceFlushFailedEvent || openAIStreamDataStartsClientOutput(trimmedData, eventType)
+			if lineStartsClientOutput && trimmedData != "[DONE]" && !openAIStreamEventTypeIsTerminal(eventType) {
+				semanticOutputSeen = true
+			}
+			// OpenAI Responses streams that terminate with an empty
+			// response.completed (no output, no usage, no error, nothing sent
+			// to the client) are silent upstream refusals: fail over instead of
+			// recording a successful 0/0 usage turn (issue #5009).
+			if (eventType == "response.completed" || eventType == "response.done") &&
+				!sawFailedEvent && !semanticOutputSeen && !clientOutputStarted &&
+				openAIResponsesCompletedEventIsEmpty(dataBytes, usage) {
+				return resultWithUsage(), newOpenAIResponsesEmptyCompletedFailoverError(c, account, upstreamRequestID)
+			}
 			if firstTokenMs == nil && lineStartsClientOutput && trimmedData != "[DONE]" {
 				ms := int(time.Since(startTime).Milliseconds())
 				firstTokenMs = &ms
diff --git a/backend/internal/service/openai_gateway_response_handling.go b/backend/internal/service/openai_gateway_response_handling.go
index cda23fa07b..d8a17b19f4 100644
--- a/backend/internal/service/openai_gateway_response_handling.go
+++ b/backend/internal/service/openai_gateway_response_handling.go
@@ -228,6 +228,7 @@ func (s *OpenAIGatewayService) handleStreamingResponseWithReasoning(ctx context.
 	clientDisconnected := false // 客户端断开后继续 drain 上游以收集 usage
 	sawTerminalEvent := false
 	sawFailedEvent := false
+	responsesSemanticOutputSeen := false
 	failedMessage := ""
 	clientOutputStarted := false
 	upstreamRequestID := strings.TrimSpace(resp.Header.Get("x-request-id"))
@@ -542,6 +543,21 @@ func (s *OpenAIGatewayService) handleStreamingResponseWithReasoning(ctx context.
 			if guardFirstOutput {
 				eventStartsClientOutput = eventStartsClientOutput || startsClientOutput
 			}
+			if startsClientOutput && !openAIStreamEventTypeIsTerminal(eventType) {
+				responsesSemanticOutputSeen = true
+			}
+			// OpenAI Responses streams that terminate with an empty
+			// response.completed (no output, no usage, no error, nothing sent
+			// to the client) are silent upstream refusals: fail over instead of
+			// recording a successful 0/0 usage turn (issue #5009).
+			if account != nil && account.Platform == PlatformOpenAI &&
+				(eventType == "response.completed" || eventType == "response.done") &&
+				!sawFailedEvent && !responsesSemanticOutputSeen && !clientOutputStarted &&
+				openAIResponsesCompletedEventIsEmpty(dataBytes, usage) {
+				sawTerminalEvent = true
+				streamEarlyErr = newOpenAIResponsesEmptyCompletedFailoverError(c, account, upstreamRequestID)
+				return
+			}
 
 			// 写入客户端（客户端断开后继续 drain 上游）
 			if !clientDisconnected {
@@ -1023,6 +1039,32 @@ func extractOpenAIUsageFromJSONBytes(body []byte) (OpenAIUsage, bool) {
 	return OpenAIUsage{}, false
 }
 
+// openAIResponsesCompletedEventIsEmpty reports whether a response.completed /
+// response.done SSE payload carries no usage, no error and no output items.
+// The accumulated usage is consulted too, because OpenAI may deliver usage on
+// an earlier event. An empty terminal event after a stream with no semantic
+// output is treated as a silent upstream refusal (issue #5009).
+func openAIResponsesCompletedEventIsEmpty(data []byte, usage *OpenAIUsage) bool {
+	if len(data) == 0 || !gjson.ValidBytes(data) {
+		return false
+	}
+	if usage != nil && (usage.InputTokens > 0 || usage.OutputTokens > 0 ||
+		usage.ImageInputTokens > 0 || usage.ImageOutputTokens > 0 ||
+		usage.CacheCreationInputTokens > 0 || usage.CacheReadInputTokens > 0) {
+		return false
+	}
+	if gjson.GetBytes(data, "usage").Exists() || gjson.GetBytes(data, "response.usage").Exists() {
+		return false
+	}
+	if gjson.GetBytes(data, "error").Exists() || gjson.GetBytes(data, "response.error").Exists() {
+		return false
+	}
+	if output := gjson.GetBytes(data, "response.output"); output.Exists() && output.IsArray() && len(output.Array()) > 0 {
+		return false
+	}
+	return true
+}
+
 func mergeHostedImageGenToolUsage(imageGen gjson.Result, usage *OpenAIUsage) {
 	if !imageGen.Exists() || !imageGen.IsObject() {
 		return
diff --git a/backend/internal/service/openai_gateway_responses_empty_completed_test.go b/backend/internal/service/openai_gateway_responses_empty_completed_test.go
new file mode 100644
index 0000000000..55bfda089c
--- /dev/null
+++ b/backend/internal/service/openai_gateway_responses_empty_completed_test.go
@@ -0,0 +1,168 @@
+//go:build unit
+
+package service
+
+import (
+	"context"
+	"errors"
+	"io"
+	"net/http"
+	"strings"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
+)
+
+// TestOpenAIResponsesEmptyCompletedFailsOver verifies that a Responses stream
+// ending with an empty response.completed (no output, no usage, no error) is
+// turned into a failover error instead of a successful empty reply (issue
+// #5009).
+func TestOpenAIResponsesEmptyCompletedFailsOver(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	upstream := &httpUpstreamRecorder{resp: &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{"Content-Type": []string{"text/event-stream"}},
+		Body: io.NopCloser(strings.NewReader(
+			"data: {\"type\":\"response.created\",\"response\":{\"id\":\"resp_empty\",\"object\":\"response\",\"status\":\"in_progress\"}}\n\n" +
+				"data: {\"type\":\"response.completed\",\"response\":{\"id\":\"resp_empty\",\"object\":\"response\",\"status\":\"completed\"}}\n\n",
+		)),
+	}}
+	svc := newOpenAIImageGenerationControlTestService(upstream)
+	c, recorder := newOpenAIImageGenerationControlTestContext(true, "codex_cli_rs/0.144.1")
+	account := newOpenAIImageGenerationControlTestAccount()
+	account.Extra = map[string]any{"openai_passthrough": true}
+
+	body := []byte(`{
+		"model":"gpt-5.6-sol",
+		"stream":true,
+		"input":[{"type":"message","role":"user","content":[{"type":"input_text","text":"continue"}]}]
+	}`)
+
+	_, err := svc.Forward(context.Background(), c, account, body)
+	require.Error(t, err)
+	var failoverErr *UpstreamFailoverError
+	require.True(t, errors.As(err, &failoverErr), "empty completed must produce UpstreamFailoverError, got: %v", err)
+	require.Equal(t, http.StatusBadGateway, failoverErr.StatusCode)
+	require.Empty(t, recorder.Body.String(), "no empty success stream may reach the client")
+}
+
+// TestOpenAIResponsesEmptyCompletedWithOutputSucceeds ensures streams with real
+// semantic output are untouched.
+func TestOpenAIResponsesEmptyCompletedWithOutputSucceeds(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	upstream := &httpUpstreamRecorder{resp: &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{"Content-Type": []string{"text/event-stream"}},
+		Body: io.NopCloser(strings.NewReader(
+			"data: {\"type\":\"response.created\",\"response\":{\"id\":\"resp_ok\",\"object\":\"response\",\"status\":\"in_progress\"}}\n\n" +
+				"data: {\"type\":\"response.output_text.delta\",\"delta\":\"hello\"}\n\n" +
+				"data: {\"type\":\"response.completed\",\"response\":{\"id\":\"resp_ok\",\"object\":\"response\",\"status\":\"completed\",\"usage\":{\"input_tokens\":10,\"output_tokens\":5,\"total_tokens\":15}}}\n\n",
+		)),
+	}}
+	svc := newOpenAIImageGenerationControlTestService(upstream)
+	c, recorder := newOpenAIImageGenerationControlTestContext(true, "codex_cli_rs/0.144.1")
+	account := newOpenAIImageGenerationControlTestAccount()
+	account.Extra = map[string]any{"openai_passthrough": true}
+
+	body := []byte(`{
+		"model":"gpt-5.6-sol",
+		"stream":true,
+		"input":[{"type":"message","role":"user","content":[{"type":"input_text","text":"continue"}]}]
+	}`)
+
+	result, err := svc.Forward(context.Background(), c, account, body)
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.Contains(t, recorder.Body.String(), "hello")
+	require.NotNil(t, result.Usage)
+	require.Equal(t, 10, result.Usage.InputTokens)
+	require.Equal(t, 5, result.Usage.OutputTokens)
+}
+
+// TestOpenAIResponsesEmptyCompletedWithUsageSucceeds ensures a completed event
+// carrying usage is not mistaken for a silent refusal even without output.
+func TestOpenAIResponsesEmptyCompletedWithUsageSucceeds(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	upstream := &httpUpstreamRecorder{resp: &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{"Content-Type": []string{"text/event-stream"}},
+		Body: io.NopCloser(strings.NewReader(
+			"data: {\"type\":\"response.created\",\"response\":{\"id\":\"resp_usage\",\"object\":\"response\",\"status\":\"in_progress\"}}\n\n" +
+				"data: {\"type\":\"response.completed\",\"response\":{\"id\":\"resp_usage\",\"object\":\"response\",\"status\":\"completed\",\"usage\":{\"input_tokens\":3,\"output_tokens\":0,\"total_tokens\":3}}}\n\n",
+		)),
+	}}
+	svc := newOpenAIImageGenerationControlTestService(upstream)
+	c, _ := newOpenAIImageGenerationControlTestContext(true, "codex_cli_rs/0.144.1")
+	account := newOpenAIImageGenerationControlTestAccount()
+	account.Extra = map[string]any{"openai_passthrough": true}
+
+	body := []byte(`{
+		"model":"gpt-5.6-sol",
+		"stream":true,
+		"input":[{"type":"message","role":"user","content":[{"type":"input_text","text":"continue"}]}]
+	}`)
+
+	result, err := svc.Forward(context.Background(), c, account, body)
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.NotNil(t, result.Usage)
+	require.Equal(t, 3, result.Usage.InputTokens)
+}
+
+func TestOpenAIResponsesCompletedEventIsEmpty(t *testing.T) {
+	cases := []struct {
+		name  string
+		data  string
+		usage *OpenAIUsage
+		want  bool
+	}{
+		{
+			name: "bare completed",
+			data: `{"type":"response.completed"}`,
+			want: true,
+		},
+		{
+			name: "completed with empty output array",
+			data: `{"type":"response.completed","response":{"id":"r1","status":"completed","output":[]}}`,
+			want: true,
+		},
+		{
+			name: "completed with usage",
+			data: `{"type":"response.completed","response":{"id":"r1","status":"completed","usage":{"input_tokens":1,"output_tokens":1}}}`,
+			want: false,
+		},
+		{
+			name: "completed with error",
+			data: `{"type":"response.completed","response":{"id":"r1","status":"completed","error":{"code":"x"}}}`,
+			want: false,
+		},
+		{
+			name: "completed with output item",
+			data: `{"type":"response.completed","response":{"id":"r1","status":"completed","output":[{"type":"message","id":"msg_1"}]}}`,
+			want: false,
+		},
+		{
+			name: "accumulated usage",
+			data: `{"type":"response.completed"}`,
+			usage: &OpenAIUsage{
+				InputTokens:  7,
+				OutputTokens: 2,
+			},
+			want: false,
+		},
+		{
+			name: "invalid json",
+			data: `{"type":`,
+			want: false,
+		},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			require.Equal(t, tc.want, openAIResponsesCompletedEventIsEmpty([]byte(tc.data), tc.usage))
+		})
+	}
+}
diff --git a/backend/internal/service/openai_gateway_service_test.go b/backend/internal/service/openai_gateway_service_test.go
index b3cb5fbd97..2c5bdba16b 100644
--- a/backend/internal/service/openai_gateway_service_test.go
+++ b/backend/internal/service/openai_gateway_service_test.go
@@ -1568,7 +1568,7 @@ func TestOpenAIStreamingTerminalAndClientCancellationDoNotQuarantineProxy(t *tes
 		Body: &openAIStreamReadThenErrorCloser{
 			reader: strings.NewReader(strings.Join([]string{
 				"event: response.completed",
-				`data: {"type":"response.completed","response":{"status":"completed","output":[]}}`,
+				`data: {"type":"response.completed","response":{"status":"completed","output":[],"usage":{"input_tokens":5,"output_tokens":3,"total_tokens":8}}}`,
 				"",
 			}, "\n")),
 			err: io.ErrUnexpectedEOF,
diff --git a/backend/internal/service/openai_silent_refusal.go b/backend/internal/service/openai_silent_refusal.go
index 27b71b7571..017c4c1f6d 100644
--- a/backend/internal/service/openai_silent_refusal.go
+++ b/backend/internal/service/openai_silent_refusal.go
@@ -16,6 +16,7 @@ const (
 	openAISilentRefusalErrorCode           = "openai_silent_refusal"
 	openAISilentRefusalUpstreamMessage     = "OpenAI upstream returned an empty completion stream with finish_reason=stop and no usage"
 	openAISilentRefusalClientMessage       = "Upstream returned an empty completion without usage; no fallback account was available"
+	openAIResponsesEmptyCompletedMessage   = "OpenAI upstream returned an empty response.completed stream with no output and no usage"
 )
 
 type openAIChatSilentRefusalDetector struct {
@@ -266,6 +267,43 @@ func newOpenAISilentRefusalFailoverError(c *gin.Context, account *Account, upstr
 	}
 }
 
+// newOpenAIResponsesEmptyCompletedFailoverError marks an empty
+// response.completed terminal event as a retryable upstream anomaly. OpenAI
+// Responses streams that deliver only response.created + response.completed
+// with no output, no usage and no error are treated as silent upstream
+// refusals rather than successful empty replies (issue #5009).
+func newOpenAIResponsesEmptyCompletedFailoverError(c *gin.Context, account *Account, upstreamRequestID string) *UpstreamFailoverError {
+	accountID := int64(0)
+	accountName := ""
+	platform := PlatformOpenAI
+	if account != nil {
+		accountID = account.ID
+		accountName = account.Name
+		platform = account.Platform
+	}
+
+	setOpsUpstreamError(c, http.StatusBadGateway, openAIResponsesEmptyCompletedMessage, "")
+	appendOpsUpstreamError(c, OpsUpstreamErrorEvent{
+		Platform:           platform,
+		AccountID:          accountID,
+		AccountName:        accountName,
+		UpstreamStatusCode: http.StatusBadGateway,
+		UpstreamRequestID:  upstreamRequestID,
+		Kind:               "failover",
+		Message:            openAIResponsesEmptyCompletedMessage,
+	})
+
+	headers := http.Header{}
+	if strings.TrimSpace(upstreamRequestID) != "" {
+		headers.Set("x-request-id", strings.TrimSpace(upstreamRequestID))
+	}
+	return &UpstreamFailoverError{
+		StatusCode:      http.StatusBadGateway,
+		ResponseBody:    openAISilentRefusalErrorBody(),
+		ResponseHeaders: headers,
+	}
+}
+
 func openAISilentRefusalErrorBody() []byte {
 	body, err := json.Marshal(map[string]any{
 		"error": map[string]any{