diff --git a/backend/internal/server/api_contract_test.go b/backend/internal/server/api_contract_test.go
index 7f3b25f763..2bca68d3be 100644
--- a/backend/internal/server/api_contract_test.go
+++ b/backend/internal/server/api_contract_test.go
@@ -886,7 +886,7 @@ func TestAPIContracts(t *testing.T) {
 						"invitation_code_enabled": false,
 						"home_content": "",
 					"hide_ccs_import_button": false,
-					"grok_default_text_model": "grok-4.5",
+					"grok_default_text_model": "grok-4.6",
 					"grok_default_base_url_mode": "cli",
 					"grok_cross_client_model_map_enabled": true,
 					"purchase_subscription_enabled": false,
@@ -1169,7 +1169,7 @@ func TestAPIContracts(t *testing.T) {
 					"doc_url": "",
 					"home_content": "",
 					"hide_ccs_import_button": false,
-					"grok_default_text_model": "grok-4.5",
+					"grok_default_text_model": "grok-4.6",
 					"grok_default_base_url_mode": "cli",
 					"grok_cross_client_model_map_enabled": true,
 					"purchase_subscription_enabled": false,
diff --git a/backend/internal/service/setting_gateway_runtime.go b/backend/internal/service/setting_gateway_runtime.go
index 2f13278e3b..e7eda7c30e 100644
--- a/backend/internal/service/setting_gateway_runtime.go
+++ b/backend/internal/service/setting_gateway_runtime.go
@@ -457,6 +457,37 @@ func (s *SettingService) MigrateOpenAIAllowClaudeCodeCodexPluginSetting(ctx cont
 	return nil
 }
 
+// MigrateGrokDefaultTextModel upgrades the pre-4.6 built-in default for
+// existing installations. Explicit operator choices are left untouched.
+func (s *SettingService) MigrateGrokDefaultTextModel(ctx context.Context) error {
+	if s == nil || s.settingRepo == nil {
+		return nil
+	}
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	dbCtx, cancel := context.WithTimeout(context.WithoutCancel(ctx), codexRestrictionPolicyDBTimeout)
+	defer cancel()
+
+	value, err := s.settingRepo.GetValue(dbCtx, SettingKeyGrokDefaultTextModel)
+	if err != nil {
+		if errors.Is(err, ErrSettingNotFound) {
+			return nil
+		}
+		return fmt.Errorf("get %s setting: %w", SettingKeyGrokDefaultTextModel, err)
+	}
+	// Only migrate the value that was previously shipped as the built-in
+	// default. Any other value is an explicit operator choice or a future
+	// default and must remain unchanged.
+	if strings.TrimSpace(value) != "grok-4.5" {
+		return nil
+	}
+	if err := s.settingRepo.Set(dbCtx, SettingKeyGrokDefaultTextModel, "grok-4.6"); err != nil {
+		return fmt.Errorf("set %s setting: %w", SettingKeyGrokDefaultTextModel, err)
+	}
+	return nil
+}
+
 // MigrateCodexBodyFingerprintToSignals 把已废弃的 codex_cli_only_allow_body_engine_fingerprint
 // 开关并入引擎指纹信号列表。幂等:信号键已存在(非空)则不动;缺失时写默认种子,
 // 并把 body 路径行的 Required 设为旧 body 开关的值(旧 true ⇒ 勾上 body 行)。
diff --git a/backend/internal/service/setting_service_codex_policy_test.go b/backend/internal/service/setting_service_codex_policy_test.go
index 1c17b91ef8..e426dea2c5 100644
--- a/backend/internal/service/setting_service_codex_policy_test.go
+++ b/backend/internal/service/setting_service_codex_policy_test.go
@@ -202,3 +202,34 @@ func TestMigrateCodexBodyFingerprintToSignals(t *testing.T) {
 		require.Equal(t, openai.DefaultEngineFingerprintSignalsJSON(), repo.values[SettingKeyCodexCLIOnlyEngineFingerprintSignals])
 	})
 }
+
+func TestMigrateGrokDefaultTextModel(t *testing.T) {
+	t.Run("upgrades legacy built-in default", func(t *testing.T) {
+		repo := &codexPolicyMigrationRepoStub{values: map[string]string{
+			SettingKeyGrokDefaultTextModel: "grok-4.5",
+		}}
+		svc := NewSettingService(repo, &config.Config{})
+		require.NoError(t, svc.MigrateGrokDefaultTextModel(context.Background()))
+		require.Equal(t, "grok-4.6", repo.values[SettingKeyGrokDefaultTextModel])
+		require.Equal(t, "grok-4.6", repo.sets[SettingKeyGrokDefaultTextModel])
+	})
+
+	t.Run("does not overwrite an explicit model", func(t *testing.T) {
+		repo := &codexPolicyMigrationRepoStub{values: map[string]string{
+			SettingKeyGrokDefaultTextModel: "grok-4.3",
+		}}
+		svc := NewSettingService(repo, &config.Config{})
+		require.NoError(t, svc.MigrateGrokDefaultTextModel(context.Background()))
+		require.Equal(t, "grok-4.3", repo.values[SettingKeyGrokDefaultTextModel])
+		_, wrote := repo.sets[SettingKeyGrokDefaultTextModel]
+		require.False(t, wrote)
+	})
+
+	t.Run("missing setting is left for normal defaults", func(t *testing.T) {
+		repo := &codexPolicyMigrationRepoStub{values: map[string]string{}}
+		svc := NewSettingService(repo, &config.Config{})
+		require.NoError(t, svc.MigrateGrokDefaultTextModel(context.Background()))
+		_, wrote := repo.sets[SettingKeyGrokDefaultTextModel]
+		require.False(t, wrote)
+	})
+}
diff --git a/backend/internal/service/wire.go b/backend/internal/service/wire.go
index 88c3a1f185..2e34ce7b9c 100644
--- a/backend/internal/service/wire.go
+++ b/backend/internal/service/wire.go
@@ -745,6 +745,9 @@ func ProvideSettingService(settingRepo SettingRepository, groupRepo GroupReposit
 	if err := svc.MigrateCodexBodyFingerprintToSignals(context.Background()); err != nil {
 		logger.LegacyPrintf("service.setting", "Warning: migrate codex body fingerprint to signals failed: %v", err)
 	}
+	if err := svc.MigrateGrokDefaultTextModel(context.Background()); err != nil {
+		logger.LegacyPrintf("service.setting", "Warning: migrate Grok default text model failed: %v", err)
+	}
 	antigravity.SetUserAgentVersionResolver(svc.GetAntigravityUserAgentVersion)
 	// enforceCodexIdentityHeaders 是所有 Codex 出站路径共用的纯函数收口点，拿不到 ctx，
 	// 故注入无参解析器；解析器内部自带 60s TTL 缓存，热路径不触库。