diff --git a/backend/internal/domain/constants.go b/backend/internal/domain/constants.go
index cd821165a4..6500502014 100644
--- a/backend/internal/domain/constants.go
+++ b/backend/internal/domain/constants.go
@@ -105,11 +105,11 @@ var DefaultAntigravityModelMapping = map[string]string{
 	"claude-opus-4-6":            "claude-opus-4-6-thinking", // 简称映射
 	"claude-opus-4-5-thinking":   "claude-opus-4-6-thinking", // 迁移旧模型
 	"claude-sonnet-4-6":          "claude-sonnet-4-6",
-	"claude-sonnet-4-5":          "claude-sonnet-4-5",
-	"claude-sonnet-4-5-thinking": "claude-sonnet-4-5-thinking",
+	"claude-sonnet-4-5":          "claude-sonnet-4-6", // 迁移旧模型
+	"claude-sonnet-4-5-thinking": "claude-sonnet-4-6", // 迁移旧模型
 	// Claude 详细版本 ID 映射
 	"claude-opus-4-5-20251101":   "claude-opus-4-6-thinking", // 迁移旧模型
-	"claude-sonnet-4-5-20250929": "claude-sonnet-4-5",
+	"claude-sonnet-4-5-20250929": "claude-sonnet-4-6",        // 迁移旧模型
 	// Claude Haiku → Sonnet（无 Haiku 支持）
 	"claude-haiku-4-5":          "claude-sonnet-4-6",
 	"claude-haiku-4-5-20251001": "claude-sonnet-4-6",
diff --git a/backend/internal/domain/constants_test.go b/backend/internal/domain/constants_test.go
index e847e22f30..7cfcd7fa51 100644
--- a/backend/internal/domain/constants_test.go
+++ b/backend/internal/domain/constants_test.go
@@ -43,6 +43,20 @@ func TestDefaultAntigravityModelMapping_ContainsNewClaudeModels(t *testing.T) {
 	}
 }
 
+func TestDefaultAntigravityModelMapping_MigratesLegacySonnet45(t *testing.T) {
+	t.Parallel()
+
+	for _, model := range []string{
+		"claude-sonnet-4-5",
+		"claude-sonnet-4-5-thinking",
+		"claude-sonnet-4-5-20250929",
+	} {
+		if got := DefaultAntigravityModelMapping[model]; got != "claude-sonnet-4-6" {
+			t.Fatalf("expected legacy model %q to map to claude-sonnet-4-6, got %q", model, got)
+		}
+	}
+}
+
 func TestDefaultAntigravityModelMapping_Gemini31ProAliases(t *testing.T) {
 	t.Parallel()
 
diff --git a/backend/internal/service/account_test_service.go b/backend/internal/service/account_test_service.go
index 451f90db16..e7ce083ff5 100644
--- a/backend/internal/service/account_test_service.go
+++ b/backend/internal/service/account_test_service.go
@@ -43,8 +43,9 @@ import (
 var sseDataPrefix = regexp.MustCompile(`^data:\s*`)
 
 const (
-	testClaudeAPIURL   = "https://api.anthropic.com/v1/messages?beta=true"
-	chatgptCodexAPIURL = "https://chatgpt.com/backend-api/codex/responses"
+	testClaudeAPIURL            = "https://api.anthropic.com/v1/messages?beta=true"
+	chatgptCodexAPIURL          = "https://chatgpt.com/backend-api/codex/responses"
+	defaultAntigravityTestModel = "claude-sonnet-4-6"
 )
 
 // TestEvent represents a SSE event for account testing
@@ -2311,11 +2312,7 @@ func (s *AccountTestService) routeAntigravityTest(c *gin.Context, account *Accou
 func (s *AccountTestService) testAntigravityAccountConnection(c *gin.Context, account *Account, modelID string) error {
 	ctx := c.Request.Context()
 
-	// 默认模型：Claude 使用 claude-sonnet-4-5，Gemini 使用 gemini-3-pro-preview
-	testModelID := modelID
-	if testModelID == "" {
-		testModelID = "claude-sonnet-4-5"
-	}
+	testModelID := antigravityConnectionTestModel(modelID)
 
 	if s.antigravityGatewayService == nil {
 		return s.sendErrorAndEnd(c, "Antigravity gateway service not configured")
@@ -2346,6 +2343,13 @@ func (s *AccountTestService) testAntigravityAccountConnection(c *gin.Context, ac
 	return nil
 }
 
+func antigravityConnectionTestModel(modelID string) string {
+	if modelID == "" {
+		return defaultAntigravityTestModel
+	}
+	return modelID
+}
+
 // buildGeminiAPIKeyRequest builds request for Gemini API Key accounts
 func (s *AccountTestService) buildGeminiAPIKeyRequest(ctx context.Context, account *Account, modelID string, payload []byte) (*http.Request, error) {
 	apiKey := account.GetCredential("api_key")
diff --git a/backend/internal/service/account_test_service_antigravity_test.go b/backend/internal/service/account_test_service_antigravity_test.go
new file mode 100644
index 0000000000..b3362f3f69
--- /dev/null
+++ b/backend/internal/service/account_test_service_antigravity_test.go
@@ -0,0 +1,16 @@
+//go:build unit
+
+package service
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestAntigravityConnectionTestModel(t *testing.T) {
+	t.Parallel()
+
+	require.Equal(t, "claude-sonnet-4-6", antigravityConnectionTestModel(""))
+	require.Equal(t, "gemini-3.1-pro-preview", antigravityConnectionTestModel("gemini-3.1-pro-preview"))
+}
diff --git a/backend/internal/service/antigravity_credits_overages_test.go b/backend/internal/service/antigravity_credits_overages_test.go
index 7a5224daf3..bdba5cec7b 100644
--- a/backend/internal/service/antigravity_credits_overages_test.go
+++ b/backend/internal/service/antigravity_credits_overages_test.go
@@ -239,7 +239,7 @@ func TestAntigravityRetryLoop_ModelRateLimited_InjectsCredits(t *testing.T) {
 		Extra: map[string]any{
 			"allow_overages": true,
 			modelRateLimitsKey: map[string]any{
-				"claude-sonnet-4-5": map[string]any{
+				"claude-sonnet-4-6": map[string]any{
 					"rate_limited_at":     time.Now().UTC().Format(time.RFC3339),
 					"rate_limit_reset_at": time.Now().Add(30 * time.Minute).UTC().Format(time.RFC3339),
 				},
@@ -290,7 +290,7 @@ func TestAntigravityRetryLoop_CreditsExhausted_DoesNotInject(t *testing.T) {
 		Extra: map[string]any{
 			"allow_overages": true,
 			modelRateLimitsKey: map[string]any{
-				"claude-sonnet-4-5": map[string]any{
+				"claude-sonnet-4-6": map[string]any{
 					"rate_limited_at":     time.Now().UTC().Format(time.RFC3339),
 					"rate_limit_reset_at": time.Now().Add(30 * time.Minute).UTC().Format(time.RFC3339),
 				},
@@ -355,7 +355,7 @@ func TestAntigravityRetryLoop_CreditErrorMarksExhausted(t *testing.T) {
 		Extra: map[string]any{
 			"allow_overages": true,
 			modelRateLimitsKey: map[string]any{
-				"claude-sonnet-4-5": map[string]any{
+				"claude-sonnet-4-6": map[string]any{
 					"rate_limited_at":     time.Now().UTC().Format(time.RFC3339),
 					"rate_limit_reset_at": time.Now().Add(30 * time.Minute).UTC().Format(time.RFC3339),
 				},
diff --git a/backend/internal/service/antigravity_model_mapping_test.go b/backend/internal/service/antigravity_model_mapping_test.go
index 62ff2e295d..0f86aa4a9c 100644
--- a/backend/internal/service/antigravity_model_mapping_test.go
+++ b/backend/internal/service/antigravity_model_mapping_test.go
@@ -69,10 +69,10 @@ func TestAntigravityGatewayService_GetMappedModel(t *testing.T) {
 			expected:       "claude-sonnet-4-6",
 		},
 		{
-			name:           "默认映射 - claude-sonnet-4-5-20250929 → claude-sonnet-4-5",
+			name:           "默认映射 - claude-sonnet-4-5-20250929 → claude-sonnet-4-6",
 			requestedModel: "claude-sonnet-4-5-20250929",
 			accountMapping: nil,
-			expected:       "claude-sonnet-4-5",
+			expected:       "claude-sonnet-4-6",
 		},
 
 		// 3. 默认映射中的透传（映射到自己）
@@ -89,10 +89,10 @@ func TestAntigravityGatewayService_GetMappedModel(t *testing.T) {
 			expected:       "claude-sonnet-4-6",
 		},
 		{
-			name:           "默认映射透传 - claude-sonnet-4-5",
+			name:           "默认映射 - claude-sonnet-4-5 → claude-sonnet-4-6",
 			requestedModel: "claude-sonnet-4-5",
 			accountMapping: nil,
-			expected:       "claude-sonnet-4-5",
+			expected:       "claude-sonnet-4-6",
 		},
 		{
 			name:           "默认映射透传 - claude-opus-4-8",
@@ -113,10 +113,10 @@ func TestAntigravityGatewayService_GetMappedModel(t *testing.T) {
 			expected:       "claude-opus-4-6-thinking",
 		},
 		{
-			name:           "默认映射透传 - claude-sonnet-4-5-thinking",
+			name:           "默认映射 - claude-sonnet-4-5-thinking → claude-sonnet-4-6",
 			requestedModel: "claude-sonnet-4-5-thinking",
 			accountMapping: nil,
-			expected:       "claude-sonnet-4-5-thinking",
+			expected:       "claude-sonnet-4-6",
 		},
 		{
 			name:           "默认映射透传 - gemini-2.5-flash",
diff --git a/backend/internal/service/antigravity_rate_limit_test.go b/backend/internal/service/antigravity_rate_limit_test.go
index c9b4298291..7a06a4e49e 100644
--- a/backend/internal/service/antigravity_rate_limit_test.go
+++ b/backend/internal/service/antigravity_rate_limit_test.go
@@ -206,7 +206,7 @@ func TestHandleUpstreamError_429_NonModelRateLimit(t *testing.T) {
 	// 但 429 兜底逻辑会使用 requestedModel 设置模型级限流
 	require.Nil(t, result)
 	require.Len(t, repo.modelRateLimitCalls, 1)
-	require.Equal(t, "claude-sonnet-4-5", repo.modelRateLimitCalls[0].modelKey)
+	require.Equal(t, "claude-sonnet-4-6", repo.modelRateLimitCalls[0].modelKey)
 }
 
 // TestHandleUpstreamError_429_NonModelRateLimit_UsesMappedModelKey 测试 429 非模型限流场景
@@ -844,17 +844,28 @@ func TestSetAntigravityModelRateLimits_GeminiWritesFamilyScope(t *testing.T) {
 	require.Equal(t, antigravityGeminiModelRateLimitKey, repo.modelRateLimitCalls[1].modelKey)
 }
 
-func TestSetAntigravityModelRateLimits_ClaudeDoesNotWriteGeminiScope(t *testing.T) {
+func TestSetAntigravityModelRateLimits_DoesNotDoubleMapCustomChain(t *testing.T) {
 	repo := &stubAntigravityAccountRepo{}
 	svc := &AntigravityGatewayService{}
-	account := &Account{ID: 790, Platform: PlatformAntigravity}
+	account := &Account{
+		ID:       790,
+		Platform: PlatformAntigravity,
+		Credentials: map[string]any{
+			"model_mapping": map[string]any{
+				"custom-sonnet":     "claude-sonnet-4-5",
+				"claude-sonnet-4-5": "claude-sonnet-4-6",
+			},
+		},
+	}
 	resetAt := time.Now().Add(30 * time.Second)
+	canonicalModel := resolveFinalAntigravityModelKey(context.Background(), account, "custom-sonnet")
+	require.Equal(t, "claude-sonnet-4-5", canonicalModel)
 
 	success := svc.setAntigravityModelRateLimits(
 		context.Background(),
 		repo,
 		account,
-		"claude-sonnet-4-5",
+		canonicalModel,
 		"[test]",
 		429,
 		resetAt,
@@ -866,6 +877,33 @@ func TestSetAntigravityModelRateLimits_ClaudeDoesNotWriteGeminiScope(t *testing.
 	require.Equal(t, "claude-sonnet-4-5", repo.modelRateLimitCalls[0].modelKey)
 }
 
+func TestSetModelRateLimitAndClearSession_UsesUpstreamReportedModelMetadata(t *testing.T) {
+	repo := &stubAntigravityAccountRepo{}
+	svc := &AntigravityGatewayService{accountRepo: repo}
+	account := &Account{
+		ID:       791,
+		Platform: PlatformAntigravity,
+		Credentials: map[string]any{
+			"model_mapping": map[string]any{
+				"claude-sonnet-4-5": "claude-sonnet-4-6",
+			},
+		},
+	}
+
+	svc.setModelRateLimitAndClearSession(&handleModelRateLimitParams{
+		ctx:        context.Background(),
+		prefix:     "[test]",
+		account:    account,
+		statusCode: 429,
+	}, &antigravitySmartRetryInfo{
+		RetryDelay: 30 * time.Second,
+		ModelName:  "claude-sonnet-4-5",
+	})
+
+	require.Len(t, repo.modelRateLimitCalls, 1)
+	require.Equal(t, "claude-sonnet-4-5", repo.modelRateLimitCalls[0].modelKey)
+}
+
 func TestAntigravityRetryLoop_PreCheck_SwitchesWhenRateLimited(t *testing.T) {
 	upstream := &recordingOKUpstream{}
 	account := &Account{
@@ -877,7 +915,7 @@ func TestAntigravityRetryLoop_PreCheck_SwitchesWhenRateLimited(t *testing.T) {
 		Concurrency: 1,
 		Extra: map[string]any{
 			modelRateLimitsKey: map[string]any{
-				"claude-sonnet-4-5": map[string]any{
+				"claude-sonnet-4-6": map[string]any{
 					"rate_limit_reset_at": time.Now().Add(2 * time.Second).Format(time.RFC3339),
 				},
 			},
@@ -920,7 +958,7 @@ func TestAntigravityRetryLoop_PreCheck_SwitchesWhenRemainingLong(t *testing.T) {
 		Concurrency: 1,
 		Extra: map[string]any{
 			modelRateLimitsKey: map[string]any{
-				"claude-sonnet-4-5": map[string]any{
+				"claude-sonnet-4-6": map[string]any{
 					"rate_limit_reset_at": time.Now().Add(11 * time.Second).Format(time.RFC3339),
 				},
 			},
diff --git a/backend/internal/service/antigravity_single_account_retry_test.go b/backend/internal/service/antigravity_single_account_retry_test.go
index 6e58ab75d2..85677e59c4 100644
--- a/backend/internal/service/antigravity_single_account_retry_test.go
+++ b/backend/internal/service/antigravity_single_account_retry_test.go
@@ -693,7 +693,7 @@ func TestAntigravityRetryLoop_PreCheck_SingleAccountRetry_SkipsRateLimit(t *test
 		Concurrency: 1,
 		Extra: map[string]any{
 			modelRateLimitsKey: map[string]any{
-				"claude-sonnet-4-5": map[string]any{
+				"claude-sonnet-4-6": map[string]any{
 					"rate_limit_reset_at": time.Now().Add(30 * time.Second).Format(time.RFC3339),
 				},
 			},
@@ -737,7 +737,7 @@ func TestAntigravityRetryLoop_PreCheck_NoSingleAccountRetry_SwitchesOnRateLimit(
 		Concurrency: 1,
 		Extra: map[string]any{
 			modelRateLimitsKey: map[string]any{
-				"claude-sonnet-4-5": map[string]any{
+				"claude-sonnet-4-6": map[string]any{
 					"rate_limit_reset_at": time.Now().Add(30 * time.Second).Format(time.RFC3339),
 				},
 			},
diff --git a/backend/internal/service/model_rate_limit_test.go b/backend/internal/service/model_rate_limit_test.go
index 430d91baf6..3293853d74 100644
--- a/backend/internal/service/model_rate_limit_test.go
+++ b/backend/internal/service/model_rate_limit_test.go
@@ -255,7 +255,7 @@ func TestIsModelRateLimited_OpenAIImageGenerationIntentBlocksTextModelImageTool(
 	require.True(t, account.isModelRateLimitedWithContext(WithOpenAIImageGenerationIntent(context.Background()), "gpt-5.4"))
 }
 
-func TestIsModelRateLimited_Antigravity_ThinkingAffectsModelKey(t *testing.T) {
+func TestIsModelRateLimited_Antigravity_LegacySonnetUsesCanonicalModelKey(t *testing.T) {
 	now := time.Now()
 	future := now.Add(10 * time.Minute).Format(time.RFC3339)
 
@@ -263,7 +263,7 @@ func TestIsModelRateLimited_Antigravity_ThinkingAffectsModelKey(t *testing.T) {
 		Platform: PlatformAntigravity,
 		Extra: map[string]any{
 			modelRateLimitsKey: map[string]any{
-				"claude-sonnet-4-5-thinking": map[string]any{
+				"claude-sonnet-4-6": map[string]any{
 					"rate_limit_reset_at": future,
 				},
 			},
@@ -453,7 +453,7 @@ func TestGetRateLimitRemainingTime(t *testing.T) {
 				Platform: PlatformAntigravity,
 				Extra: map[string]any{
 					modelRateLimitsKey: map[string]any{
-						"claude-sonnet-4-5": map[string]any{
+						"claude-sonnet-4-6": map[string]any{
 							"rate_limit_reset_at": future15m,
 						},
 					},
@@ -469,7 +469,7 @@ func TestGetRateLimitRemainingTime(t *testing.T) {
 				Platform: PlatformAntigravity,
 				Extra: map[string]any{
 					modelRateLimitsKey: map[string]any{
-						"claude-sonnet-4-5": map[string]any{
+						"claude-sonnet-4-6": map[string]any{
 							"rate_limit_reset_at": future5m,
 						},
 					},