diff --git a/backend/internal/service/account_test_service.go b/backend/internal/service/account_test_service.go
index e62f459e08..31549a6b17 100644
--- a/backend/internal/service/account_test_service.go
+++ b/backend/internal/service/account_test_service.go
@@ -582,8 +582,13 @@ func (s *AccountTestService) testOpenAIAccountConnection(c *gin.Context, account
 	c.Writer.Header().Set("X-Accel-Buffering", "no")
 	c.Writer.Flush()
 
-	// Create OpenAI Responses API payload
-	payload := createOpenAITestPayload(testModelID, isOAuth)
+	// Create OpenAI Responses API payload. OAuth accounts use ChatGPT Codex
+	// upstream and must apply the same model normalization as real forwarding.
+	upstreamTestModelID := testModelID
+	if isOAuth {
+		upstreamTestModelID = normalizeOpenAIModelForUpstream(credentialAccount, testModelID)
+	}
+	payload := createOpenAITestPayload(upstreamTestModelID, isOAuth)
 	payloadBytes, _ := json.Marshal(payload)
 
 	// Send test_start event
diff --git a/backend/internal/service/account_test_service_openai_test.go b/backend/internal/service/account_test_service_openai_test.go
index af28085123..083d882ea7 100644
--- a/backend/internal/service/account_test_service_openai_test.go
+++ b/backend/internal/service/account_test_service_openai_test.go
@@ -137,6 +137,34 @@ func TestAccountTestService_OpenAISuccessPersistsSnapshotFromHeaders(t *testing.
 	require.Contains(t, recorder.Body.String(), "test_complete")
 }
 
+func TestAccountTestService_OpenAIOAuthTestNormalizesGPT56Alias(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	ctx, _ := newTestContext()
+
+	resp := newJSONResponse(http.StatusOK, "")
+	resp.Body = io.NopCloser(strings.NewReader(`data: {"type":"response.completed"}
+
+`))
+
+	upstream := &queuedHTTPUpstream{responses: []*http.Response{resp}}
+	svc := &AccountTestService{httpUpstream: upstream}
+	account := &Account{
+		ID:          90,
+		Platform:    PlatformOpenAI,
+		Type:        AccountTypeOAuth,
+		Concurrency: 1,
+		Credentials: map[string]any{"access_token": "test-token"},
+	}
+
+	err := svc.testOpenAIAccountConnection(ctx, account, "gpt-5.6", "", "")
+	require.NoError(t, err)
+	require.Len(t, upstream.requests, 1)
+
+	body, err := io.ReadAll(upstream.requests[0].Body)
+	require.NoError(t, err)
+	require.Equal(t, "gpt-5.6-sol", gjson.GetBytes(body, "model").String())
+}
+
 func TestAccountTestService_OpenAIShadowUsesParentCredentialsAndShadowModel(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	ctx, recorder := newTestContext()