diff --git a/sdk/api/handlers/openai/gitlab_duo_handler_test.go b/sdk/api/handlers/openai/gitlab_duo_handler_test.go
new file mode 100644
index 00000000..e70f7f04
--- /dev/null
+++ b/sdk/api/handlers/openai/gitlab_duo_handler_test.go
@@ -0,0 +1,143 @@
+package openai
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	internalconfig "github.com/router-for-me/CLIProxyAPI/v6/internal/config"
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/registry"
+	runtimeexecutor "github.com/router-for-me/CLIProxyAPI/v6/internal/runtime/executor"
+	_ "github.com/router-for-me/CLIProxyAPI/v6/internal/translator"
+	"github.com/router-for-me/CLIProxyAPI/v6/sdk/api/handlers"
+	coreauth "github.com/router-for-me/CLIProxyAPI/v6/sdk/cliproxy/auth"
+	sdkconfig "github.com/router-for-me/CLIProxyAPI/v6/sdk/config"
+)
+
+func TestOpenAIChatCompletionsWithGitLabDuoOpenAIGateway(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	var gotPath, gotAuthHeader, gotRealmHeader string
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotPath = r.URL.Path
+		gotAuthHeader = r.Header.Get("Authorization")
+		gotRealmHeader = r.Header.Get("X-Gitlab-Realm")
+		w.Header().Set("Content-Type", "text/event-stream")
+		_, _ = w.Write([]byte("data: {\"type\":\"response.created\",\"response\":{\"id\":\"resp_1\",\"created_at\":1710000000,\"model\":\"gpt-5-codex\"}}\n\n"))
+		_, _ = w.Write([]byte("data: {\"type\":\"response.output_text.delta\",\"delta\":\"hello from duo openai\"}\n\n"))
+		_, _ = w.Write([]byte("data: {\"type\":\"response.completed\",\"response\":{\"id\":\"resp_1\",\"created_at\":1710000000,\"model\":\"gpt-5-codex\",\"status\":\"completed\",\"output\":[{\"type\":\"message\",\"id\":\"msg_1\",\"role\":\"assistant\",\"content\":[{\"type\":\"output_text\",\"text\":\"hello from duo openai\"}]}],\"usage\":{\"input_tokens\":11,\"output_tokens\":4,\"total_tokens\":15}}}\n\n"))
+	}))
+	defer upstream.Close()
+
+	manager := registerGitLabDuoOpenAIAuth(t, upstream.URL)
+	base := handlers.NewBaseAPIHandlers(&sdkconfig.SDKConfig{}, manager)
+	h := NewOpenAIAPIHandler(base)
+	router := gin.New()
+	router.POST("/v1/chat/completions", h.ChatCompletions)
+
+	req := httptest.NewRequest(http.MethodPost, "/v1/chat/completions", strings.NewReader(`{
+		"model":"gpt-5-codex",
+		"messages":[{"role":"user","content":"hello"}]
+	}`))
+	req.Header.Set("Content-Type", "application/json")
+	resp := httptest.NewRecorder()
+	router.ServeHTTP(resp, req)
+
+	if resp.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d body=%s", resp.Code, http.StatusOK, resp.Body.String())
+	}
+	if gotPath != "/v1/proxy/openai/v1/responses" {
+		t.Fatalf("path = %q, want %q", gotPath, "/v1/proxy/openai/v1/responses")
+	}
+	if gotAuthHeader != "Bearer gateway-token" {
+		t.Fatalf("authorization = %q, want Bearer gateway-token", gotAuthHeader)
+	}
+	if gotRealmHeader != "saas" {
+		t.Fatalf("x-gitlab-realm = %q, want saas", gotRealmHeader)
+	}
+	if !strings.Contains(resp.Body.String(), `"content":"hello from duo openai"`) {
+		t.Fatalf("expected translated chat completion, got %s", resp.Body.String())
+	}
+}
+
+func TestOpenAIResponsesStreamWithGitLabDuoOpenAIGateway(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	var gotPath, gotAuthHeader string
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotPath = r.URL.Path
+		gotAuthHeader = r.Header.Get("Authorization")
+		w.Header().Set("Content-Type", "text/event-stream")
+		_, _ = w.Write([]byte("data: {\"type\":\"response.created\",\"response\":{\"id\":\"resp_1\",\"created_at\":1710000000,\"model\":\"gpt-5-codex\"}}\n\n"))
+		_, _ = w.Write([]byte("data: {\"type\":\"response.output_text.delta\",\"delta\":\"streamed duo output\"}\n\n"))
+		_, _ = w.Write([]byte("data: {\"type\":\"response.completed\",\"response\":{\"id\":\"resp_1\",\"created_at\":1710000000,\"model\":\"gpt-5-codex\",\"status\":\"completed\",\"output\":[{\"type\":\"message\",\"id\":\"msg_1\",\"role\":\"assistant\",\"content\":[{\"type\":\"output_text\",\"text\":\"streamed duo output\"}]}],\"usage\":{\"input_tokens\":10,\"output_tokens\":3,\"total_tokens\":13}}}\n\n"))
+	}))
+	defer upstream.Close()
+
+	manager := registerGitLabDuoOpenAIAuth(t, upstream.URL)
+	base := handlers.NewBaseAPIHandlers(&sdkconfig.SDKConfig{}, manager)
+	h := NewOpenAIResponsesAPIHandler(base)
+	router := gin.New()
+	router.POST("/v1/responses", h.Responses)
+
+	req := httptest.NewRequest(http.MethodPost, "/v1/responses", strings.NewReader(`{
+		"model":"gpt-5-codex",
+		"stream":true,
+		"input":"hello"
+	}`))
+	req.Header.Set("Content-Type", "application/json")
+	resp := httptest.NewRecorder()
+	router.ServeHTTP(resp, req)
+
+	if resp.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d body=%s", resp.Code, http.StatusOK, resp.Body.String())
+	}
+	if gotPath != "/v1/proxy/openai/v1/responses" {
+		t.Fatalf("path = %q, want %q", gotPath, "/v1/proxy/openai/v1/responses")
+	}
+	if gotAuthHeader != "Bearer gateway-token" {
+		t.Fatalf("authorization = %q, want Bearer gateway-token", gotAuthHeader)
+	}
+	if got := resp.Header().Get("Content-Type"); got != "text/event-stream" {
+		t.Fatalf("content-type = %q, want text/event-stream", got)
+	}
+	if !strings.Contains(resp.Body.String(), `"type":"response.output_text.delta"`) {
+		t.Fatalf("expected streamed responses delta, got %s", resp.Body.String())
+	}
+	if !strings.Contains(resp.Body.String(), `"type":"response.completed"`) {
+		t.Fatalf("expected streamed responses completion, got %s", resp.Body.String())
+	}
+}
+
+func registerGitLabDuoOpenAIAuth(t *testing.T, upstreamURL string) *coreauth.Manager {
+	t.Helper()
+
+	manager := coreauth.NewManager(nil, nil, nil)
+	manager.RegisterExecutor(runtimeexecutor.NewGitLabExecutor(&internalconfig.Config{}))
+
+	auth := &coreauth.Auth{
+		ID:       "gitlab-duo-openai-handler-test",
+		Provider: "gitlab",
+		Status:   coreauth.StatusActive,
+		Metadata: map[string]any{
+			"duo_gateway_base_url": upstreamURL,
+			"duo_gateway_token":    "gateway-token",
+			"duo_gateway_headers":  map[string]string{"X-Gitlab-Realm": "saas"},
+			"model_provider":       "openai",
+			"model_name":           "gpt-5-codex",
+		},
+	}
+	registered, err := manager.Register(context.Background(), auth)
+	if err != nil {
+		t.Fatalf("register auth: %v", err)
+	}
+
+	registry.GetGlobalRegistry().RegisterClient(registered.ID, registered.Provider, runtimeexecutor.GitLabModelsFromAuth(registered))
+	t.Cleanup(func() {
+		registry.GetGlobalRegistry().UnregisterClient(registered.ID)
+	})
+	return manager
+}