diff --git a/backend/internal/service/openai_gateway_messages.go b/backend/internal/service/openai_gateway_messages.go
index 8c5c801944..92ee773166 100644
--- a/backend/internal/service/openai_gateway_messages.go
+++ b/backend/internal/service/openai_gateway_messages.go
@@ -302,18 +302,7 @@ func (s *OpenAIGatewayService) ForwardAsAnthropic(
 	}
 	resp, err := s.httpUpstream.Do(upstreamReq, proxyURL, account.ID, account.Concurrency)
 	if err != nil {
-		safeErr := sanitizeUpstreamErrorMessage(err.Error())
-		setOpsUpstreamError(c, 0, safeErr, "")
-		appendOpsUpstreamError(c, OpsUpstreamErrorEvent{
-			Platform:           account.Platform,
-			AccountID:          account.ID,
-			AccountName:        account.Name,
-			UpstreamStatusCode: 0,
-			Kind:               "request_error",
-			Message:            safeErr,
-		})
-		writeAnthropicError(c, http.StatusBadGateway, "api_error", "Upstream request failed")
-		return nil, fmt.Errorf("upstream request failed: %s", safeErr)
+		return nil, s.handleOpenAIUpstreamTransportError(ctx, c, account, err, false)
 	}
 	defer func() { _ = resp.Body.Close() }()
 
diff --git a/backend/internal/service/openai_gateway_messages_transport_failover_test.go b/backend/internal/service/openai_gateway_messages_transport_failover_test.go
new file mode 100644
index 0000000000..a61da140f5
--- /dev/null
+++ b/backend/internal/service/openai_gateway_messages_transport_failover_test.go
@@ -0,0 +1,92 @@
+//go:build unit
+
+package service
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
+)
+
+func TestForwardAsAnthropic_TransportError_ReturnsFailoverError(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	body := []byte(`{"model":"gpt-5.4","max_tokens":32,"messages":[{"role":"user","content":"hello"}],"stream":false}`)
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/messages", bytes.NewReader(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	upstream := &httpUpstreamRecorder{
+		err: errors.New(`dial tcp 1.2.3.4:443: connect: connection refused`),
+	}
+	svc := &OpenAIGatewayService{
+		cfg:          rawChatCompletionsTestConfig(),
+		httpUpstream: upstream,
+	}
+
+	account := rawChatCompletionsTestAccount()
+	_, err := svc.ForwardAsAnthropic(context.Background(), c, account, body, "", "")
+
+	require.Error(t, err)
+	var failoverErr *UpstreamFailoverError
+	require.True(t, errors.As(err, &failoverErr), "transport error should return UpstreamFailoverError for handler failover, got: %T", err)
+	require.Equal(t, http.StatusBadGateway, failoverErr.StatusCode)
+}
+
+func TestForwardAsAnthropic_TransportError_DoesNotWriteResponse(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	body := []byte(`{"model":"gpt-5.4","max_tokens":32,"messages":[{"role":"user","content":"hello"}],"stream":false}`)
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/messages", bytes.NewReader(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	upstream := &httpUpstreamRecorder{
+		err: errors.New(`read tcp: connection reset by peer`),
+	}
+	svc := &OpenAIGatewayService{
+		cfg:          rawChatCompletionsTestConfig(),
+		httpUpstream: upstream,
+	}
+
+	account := rawChatCompletionsTestAccount()
+	_, _ = svc.ForwardAsAnthropic(context.Background(), c, account, body, "", "")
+
+	require.Equal(t, http.StatusOK, rec.Code, "transport error must not write HTTP response — handler owns the response for failover")
+	require.Empty(t, rec.Body.String(), "response body must be empty so handler can write the correct error or failover")
+}
+
+func TestForwardAsAnthropic_TransportError_ClientCanceled_NoFailover(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	body := []byte(`{"model":"gpt-5.4","max_tokens":32,"messages":[{"role":"user","content":"hello"}],"stream":false}`)
+	rec := httptest.NewRecorder()
+	cancelCtx, cancel := context.WithCancel(context.Background())
+	cancel()
+	c, _ := gin.CreateTestContext(rec)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/messages", bytes.NewReader(body)).WithContext(cancelCtx)
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	upstream := &httpUpstreamRecorder{
+		err: context.Canceled,
+	}
+	svc := &OpenAIGatewayService{
+		cfg:          rawChatCompletionsTestConfig(),
+		httpUpstream: upstream,
+	}
+
+	account := rawChatCompletionsTestAccount()
+	_, err := svc.ForwardAsAnthropic(context.Background(), c, account, body, "", "")
+
+	require.Error(t, err)
+	var failoverErr *UpstreamFailoverError
+	require.False(t, errors.As(err, &failoverErr), "client-canceled transport error should NOT trigger failover")
+}