diff --git a/relay/channel/openai/relay_responses.go b/relay/channel/openai/relay_responses.go
index ceca1af3b3..a1a45f2a96 100644
--- a/relay/channel/openai/relay_responses.go
+++ b/relay/channel/openai/relay_responses.go
@@ -131,6 +131,12 @@ func OaiResponsesStreamHandler(c *gin.Context, info *relaycommon.RelayInfo, resp
 				imageCounter.Commit(info)
 				imageCommitted = true
 			}
+			// Responses SSE has no "data: [DONE]" sentinel: after this event the
+			// upstream simply idles until it closes the socket. Mark completion here,
+			// otherwise the end reason is decided by a race between upstream EOF and
+			// the client closing its connection right after the final event, which
+			// mislabels finished streams as client_gone (#6649).
+			sr.Done()
 		case "response.failed", "response.incomplete", "response.cancelled", "response.canceled":
 			if !imageCommitted {
 				imageCounter.Reset()
diff --git a/relay/channel/openai/relay_responses_stream_test.go b/relay/channel/openai/relay_responses_stream_test.go
new file mode 100644
index 0000000000..4d3ccf00db
--- /dev/null
+++ b/relay/channel/openai/relay_responses_stream_test.go
@@ -0,0 +1,75 @@
+package openai
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/QuantumNous/new-api/constant"
+	relaycommon "github.com/QuantumNous/new-api/relay/common"
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// Upstreams for /v1/responses do not send a "data: [DONE]" sentinel; the stream
+// simply idles after "response.completed" until the upstream closes the socket.
+// The handler must therefore mark completion itself, otherwise the end reason is
+// decided by a race between upstream EOF and the client closing its connection
+// right after the final event, which mislabels finished streams as client_gone
+// (issue #6649).
+func TestOaiResponsesStreamHandlerMarksDoneOnCompleted(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	if constant.StreamingTimeout == 0 {
+		constant.StreamingTimeout = 30
+	}
+
+	pr, pw := io.Pipe()
+	t.Cleanup(func() {
+		_ = pr.Close()
+		_ = pw.Close()
+	})
+
+	recorder := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(recorder)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/responses", nil)
+
+	resp := &http.Response{Body: pr}
+	info := &relaycommon.RelayInfo{
+		DisablePing: true,
+		ChannelMeta: &relaycommon.ChannelMeta{},
+	}
+
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		usage, apiErr := OaiResponsesStreamHandler(c, info, resp)
+		assert.Nil(t, apiErr)
+		if assert.NotNil(t, usage) {
+			assert.Equal(t, 5, usage.PromptTokens)
+			assert.Equal(t, 7, usage.CompletionTokens)
+		}
+	}()
+
+	_, err := fmt.Fprint(pw, "data: {\"type\":\"response.output_text.delta\",\"delta\":\"hi\"}\n")
+	require.NoError(t, err)
+	_, err = fmt.Fprint(pw, "data: {\"type\":\"response.completed\",\"response\":{\"usage\":{\"input_tokens\":5,\"output_tokens\":7,\"total_tokens\":12}}}\n")
+	require.NoError(t, err)
+
+	// Keep the pipe open: the handler must finish on the terminal event alone,
+	// without waiting for upstream EOF.
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Fatal("handler did not return after response.completed (still waiting for upstream EOF)")
+	}
+
+	require.NotNil(t, info.StreamStatus)
+	assert.Equal(t, relaycommon.StreamEndReasonDone, info.StreamStatus.EndReason)
+
+	body := recorder.Body.String()
+	assert.Contains(t, body, "response.completed", "terminal event must still be forwarded to the client")
+}