diff --git a/README_CN.md b/README_CN.md
index 3116e7c5fa..725e27d844 100644
--- a/README_CN.md
+++ b/README_CN.md
@@ -227,6 +227,30 @@ underscores_in_headers on;
 
 Nginx 默认会丢弃名称中含下划线的请求头（如 `session_id`），这会导致多账号环境下的粘性会话功能失效。
 
+## Codex Fast/Flex 策略说明
+
+管理员后台的 `系统设置 -> 网关服务 -> OpenAI Fast/Flex 策略` 只负责处理请求体中的 `service_tier`，不会修改 Codex 客户端的模型目录，也不会让 Codex UI 自动出现 Speed 或 `/fast` 选项。
+
+策略支持以下处理方式：
+
+- `pass`：保留客户端传入的 `service_tier`；`fast` 会规范为上游使用的 `priority`。
+- `filter`：移除 `service_tier`，按普通优先级请求。
+- `block`：拒绝匹配的 Fast/Flex 请求。
+- `force_priority`：将匹配请求强制设置为 `priority`，会按 Priority/Fast 价格计费。为避免升级后改变既有规则语义，`all` 只匹配显式存在的 tier；如需让省略 `service_tier` 的 OpenAI 请求也强制升级，必须新增 `service_tier=missing + force_priority` 规则。非 OpenAI 平台不会执行缺省 tier 注入。这种方式可以让请求实际使用 Fast，但 Codex UI 仍可能不显示 Fast 状态。
+
+Codex 的 Fast 入口由客户端模型目录驱动。只有当前模型目录声明了 `additional_speed_tiers: ["fast"]` 和对应的 `service_tiers`，Codex 才会显示 `/fast`。通过 API Key 或自定义模型提供商连接 Sub2API 时，如果模型目录没有这些字段，即使后台配置了 `force_priority`，重启 Codex 后也不会出现 Speed 选项。
+
+客户端可在 `~/.codex/config.toml` 中直接指定默认请求级别：
+
+```toml
+service_tier = "fast"
+
+[features]
+fast_mode = true
+```
+
+其中 `service_tier = "fast"` 会让请求携带 Fast 设置；`features.fast_mode` 只启用客户端 Fast 功能。模型目录没有声明 Fast 能力时，`/fast` 仍可能不显示。可通过 Sub2API 使用记录确认最终 `service_tier` 是否为 `priority`。
+
 ---
 
 ## 部署方式
diff --git a/backend/internal/service/openai_fast_policy_test.go b/backend/internal/service/openai_fast_policy_test.go
index a29e7ffd21..6a0a2080a5 100644
--- a/backend/internal/service/openai_fast_policy_test.go
+++ b/backend/internal/service/openai_fast_policy_test.go
@@ -205,6 +205,64 @@ func TestApplyOpenAIFastPolicyToBody_DefaultPassesPriorityAndFast(t *testing.T)
 	require.Equal(t, string(body), string(updated))
 }
 
+func TestApplyOpenAIFastPolicyToBody_ForcePriorityInjectsMissingTier(t *testing.T) {
+	settings := &OpenAIFastPolicySettings{
+		Rules: []OpenAIFastPolicyRule{{
+			ServiceTier: OpenAIFastTierMissing,
+			Action:      OpenAIFastPolicyActionForcePriority,
+			Scope:       BetaPolicyScopeAll,
+			UserIDs:     []int64{42},
+		}},
+	}
+	svc := newOpenAIGatewayServiceWithSettings(t, settings)
+	account := &Account{Platform: PlatformOpenAI, Type: AccountTypeOAuth}
+	body := []byte(`{"model":"gpt-5.5"}`)
+
+	matchingCtx := context.WithValue(context.Background(), ctxkey.UserID, int64(42))
+	updated, err := svc.applyOpenAIFastPolicyToBody(matchingCtx, account, "gpt-5.5", body)
+	require.NoError(t, err)
+	require.Equal(t, OpenAIFastTierPriority, gjson.GetBytes(updated, "service_tier").String())
+
+	otherCtx := context.WithValue(context.Background(), ctxkey.UserID, int64(43))
+	updated, err = svc.applyOpenAIFastPolicyToBody(otherCtx, account, "gpt-5.5", body)
+	require.NoError(t, err)
+	require.False(t, gjson.GetBytes(updated, "service_tier").Exists())
+}
+
+func TestApplyOpenAIFastPolicyToBody_LegacyAllRuleDoesNotInjectMissingTier(t *testing.T) {
+	settings := &OpenAIFastPolicySettings{
+		Rules: []OpenAIFastPolicyRule{{
+			ServiceTier: OpenAIFastTierAny,
+			Action:      OpenAIFastPolicyActionForcePriority,
+			Scope:       BetaPolicyScopeAll,
+		}},
+	}
+	svc := newOpenAIGatewayServiceWithSettings(t, settings)
+	account := &Account{Platform: PlatformOpenAI, Type: AccountTypeAPIKey}
+	body := []byte(`{"model":"gpt-5.5"}`)
+
+	updated, err := svc.applyOpenAIFastPolicyToBody(context.Background(), account, "gpt-5.5", body)
+
+	require.NoError(t, err)
+	require.Equal(t, string(body), string(updated))
+
+	// Explicitly selected tiers continue to be forced by the existing rule.
+	body = []byte(`{"model":"gpt-5.5","service_tier":"flex"}`)
+	updated, err = svc.applyOpenAIFastPolicyToBody(context.Background(), account, "gpt-5.5", body)
+	require.NoError(t, err)
+	require.Equal(t, OpenAIFastTierPriority, gjson.GetBytes(updated, "service_tier").String())
+}
+
+func TestApplyOpenAIFastPolicyToBody_MissingTierIgnoresNonForceRule(t *testing.T) {
+	svc := newOpenAIGatewayServiceWithSettings(t, openAIFastFilterPriorityPolicy())
+	account := &Account{Platform: PlatformOpenAI, Type: AccountTypeAPIKey}
+	body := []byte(`{"model":"gpt-5.5"}`)
+
+	updated, err := svc.applyOpenAIFastPolicyToBody(context.Background(), account, "gpt-5.5", body)
+	require.NoError(t, err)
+	require.Equal(t, string(body), string(updated))
+}
+
 func TestApplyOpenAIFastPolicyToBody_ExplicitFilterRemovesField(t *testing.T) {
 	svc := newOpenAIGatewayServiceWithSettings(t, openAIFastFilterPriorityPolicy())
 	account := &Account{Platform: PlatformOpenAI, Type: AccountTypeAPIKey}
@@ -505,16 +563,23 @@ func TestSetOpenAIFastPolicySettings_Validation(t *testing.T) {
 				Action:      BetaPolicyActionPass,
 				Scope:       BetaPolicyScopeAll,
 			},
+			{
+				ServiceTier: OpenAIFastTierMissing,
+				Action:      OpenAIFastPolicyActionForcePriority,
+				Scope:       BetaPolicyScopeAll,
+			},
 		},
 	})
 	require.NoError(t, err)
 
 	got, err := svc.GetOpenAIFastPolicySettings(context.Background())
 	require.NoError(t, err)
-	require.Len(t, got.Rules, 2)
+	require.Len(t, got.Rules, 3)
 	require.Equal(t, OpenAIFastTierPriority, got.Rules[0].ServiceTier)
+	require.Equal(t, OpenAIFastTierUltrafast, got.Rules[1].ServiceTier)
+	require.Equal(t, OpenAIFastTierMissing, got.Rules[2].ServiceTier)
 	require.Equal(t, OpenAIFastPolicyActionForcePriority, got.Rules[0].Action)
 	require.Equal(t, []int64{42, 43}, got.Rules[0].UserIDs)
-	require.Equal(t, OpenAIFastTierUltrafast, got.Rules[1].ServiceTier)
 	require.Equal(t, BetaPolicyActionPass, got.Rules[1].Action)
+	require.Equal(t, OpenAIFastPolicyActionForcePriority, got.Rules[2].Action)
 }
diff --git a/backend/internal/service/openai_fast_policy_ws_test.go b/backend/internal/service/openai_fast_policy_ws_test.go
index c154f32abf..7bc2d5f4dc 100644
--- a/backend/internal/service/openai_fast_policy_ws_test.go
+++ b/backend/internal/service/openai_fast_policy_ws_test.go
@@ -136,6 +136,24 @@ func TestWSResponseCreate_GroupForceInjectsMissingTier(t *testing.T) {
 	require.Equal(t, OpenAIFastTierPriority, gjson.GetBytes(updated, "service_tier").String())
 }
 
+func TestWSResponseCreate_ForcePriorityInjectsMissingTier(t *testing.T) {
+	settings := &OpenAIFastPolicySettings{
+		Rules: []OpenAIFastPolicyRule{{
+			ServiceTier: OpenAIFastTierMissing,
+			Action:      OpenAIFastPolicyActionForcePriority,
+			Scope:       BetaPolicyScopeAll,
+		}},
+	}
+	svc := newOpenAIGatewayServiceWithSettings(t, settings)
+	account := &Account{Platform: PlatformOpenAI, Type: AccountTypeOAuth}
+	frame := []byte(`{"type":"response.create","model":"gpt-5.5"}`)
+
+	updated, blocked, err := svc.applyOpenAIFastPolicyToWSResponseCreate(context.Background(), account, "gpt-5.5", frame)
+	require.NoError(t, err)
+	require.Nil(t, blocked)
+	require.Equal(t, OpenAIFastTierPriority, gjson.GetBytes(updated, "service_tier").String())
+}
+
 func TestWSResponseCreate_GroupForceDoesNotTouchOtherFrames(t *testing.T) {
 	svc := newOpenAIGatewayServiceWithSettings(t, DefaultOpenAIFastPolicySettings())
 	account := &Account{Platform: PlatformOpenAI, Type: AccountTypeOAuth}
diff --git a/backend/internal/service/openai_gateway_forward.go b/backend/internal/service/openai_gateway_forward.go
index 2a459cc286..7f899d2c34 100644
--- a/backend/internal/service/openai_gateway_forward.go
+++ b/backend/internal/service/openai_gateway_forward.go
@@ -681,6 +681,8 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 				}
 			}
 		}
+	} else if s.shouldForceOpenAIFastPriorityForMissingTier(ctx, account, upstreamModel) {
+		markPatchSet("service_tier", OpenAIFastTierPriority)
 	}
 
 	if account.UsesOpenAICodexProtocol() {
diff --git a/backend/internal/service/openai_gateway_request_body.go b/backend/internal/service/openai_gateway_request_body.go
index 3f06c5105d..e26197ed1e 100644
--- a/backend/internal/service/openai_gateway_request_body.go
+++ b/backend/internal/service/openai_gateway_request_body.go
@@ -1605,7 +1605,7 @@ func (e *OpenAIFastBlockedError) Error() string { return e.Message }
 // Matching rules:
 //   - Scope filters by account type (all / oauth / apikey / bedrock)
 //   - UserIDs, when present, filters by the trusted Sub2API user that owns the API key
-//   - ServiceTier must be empty (= any), "all", or equal the normalized tier
+//   - ServiceTier must be empty (= any), "all", "missing", or equal the normalized tier
 //   - ModelWhitelist narrows the rule to specific models; FallbackAction
 //     handles the non-matching case (default: pass)
 //   - User-specific rules take precedence over global rules; each group keeps
@@ -1638,6 +1638,18 @@ func (s *OpenAIGatewayService) evaluateOpenAIFastPolicy(ctx context.Context, acc
 	return evaluateOpenAIFastPolicyWithSettings(settings, openAIFastPolicyUserID(ctx), account, model, tier)
 }
 
+// shouldForceOpenAIFastPriorityForMissingTier reports whether a request that
+// omitted service_tier should be upgraded to priority. This is opt-in through
+// the dedicated "missing" tier matcher; legacy "all" rules continue to apply
+// only to requests that explicitly selected a recognized tier.
+func (s *OpenAIGatewayService) shouldForceOpenAIFastPriorityForMissingTier(ctx context.Context, account *Account, model string) bool {
+	if account == nil || account.Platform != PlatformOpenAI {
+		return false
+	}
+	action, _ := s.evaluateOpenAIFastPolicy(ctx, account, model, OpenAIFastTierMissing)
+	return action == OpenAIFastPolicyActionForcePriority
+}
+
 // evaluateOpenAIFastPolicyWithSettings is the pure-function core extracted so
 // long-lived sessions (e.g. WS) can prefetch settings once and avoid hitting
 // the settingService on every frame. See WSSession entry and
@@ -1660,7 +1672,11 @@ func evaluateOpenAIFastPolicyWithSettings(settings *OpenAIFastPolicySettings, us
 				continue
 			}
 			ruleTier := strings.ToLower(strings.TrimSpace(rule.ServiceTier))
-			if ruleTier != "" && ruleTier != OpenAIFastTierAny && ruleTier != tier {
+			if tier == OpenAIFastTierMissing {
+				if ruleTier != OpenAIFastTierMissing {
+					continue
+				}
+			} else if ruleTier != "" && ruleTier != OpenAIFastTierAny && ruleTier != tier {
 				continue
 			}
 			eff := BetaPolicyRule{
@@ -1765,6 +1781,13 @@ func (s *OpenAIGatewayService) applyOpenAIFastPolicyToBody(ctx context.Context,
 	}
 	rawTier := gjson.GetBytes(body, "service_tier").String()
 	if rawTier == "" {
+		if s.shouldForceOpenAIFastPriorityForMissingTier(ctx, account, model) {
+			updated, err := sjson.SetBytes(body, "service_tier", OpenAIFastTierPriority)
+			if err != nil {
+				return body, fmt.Errorf("force missing service_tier priority on body: %w", err)
+			}
+			return updated, nil
+		}
 		return body, nil
 	}
 	normTier := normalizedOpenAIServiceTierValue(rawTier)
@@ -1884,6 +1907,13 @@ func (s *OpenAIGatewayService) applyOpenAIFastPolicyToWSResponseCreate(
 	}
 	rawTier := gjson.GetBytes(frame, "service_tier").String()
 	if rawTier == "" {
+		if s.shouldForceOpenAIFastPriorityForMissingTier(ctx, account, model) {
+			updated, err := sjson.SetBytes(frame, "service_tier", OpenAIFastTierPriority)
+			if err != nil {
+				return frame, nil, fmt.Errorf("force missing service_tier priority in ws frame: %w", err)
+			}
+			return updated, nil, nil
+		}
 		return frame, nil, nil
 	}
 	normTier := normalizedOpenAIServiceTierValue(rawTier)
diff --git a/backend/internal/service/setting_features.go b/backend/internal/service/setting_features.go
index 3827790fe8..f282761b58 100644
--- a/backend/internal/service/setting_features.go
+++ b/backend/internal/service/setting_features.go
@@ -1017,6 +1017,7 @@ func (s *SettingService) SetOpenAIFastPolicySettings(ctx context.Context, settin
 	}
 	validTiers := map[string]bool{
 		OpenAIFastTierAny: true, OpenAIFastTierPriority: true, OpenAIFastTierUltrafast: true, OpenAIFastTierFlex: true,
+		OpenAIFastTierMissing: true,
 	}
 
 	for i, rule := range settings.Rules {
diff --git a/backend/internal/service/settings_view.go b/backend/internal/service/settings_view.go
index 93e7d76bcb..83c1422568 100644
--- a/backend/internal/service/settings_view.go
+++ b/backend/internal/service/settings_view.go
@@ -683,7 +683,7 @@ func DefaultBetaPolicySettings() *BetaPolicySettings {
 //   - "priority"（客户端可传 "fast"，归一化为 "priority"）：fast 模式
 //   - "ultrafast"：Codex/API 的 Ultrafast 档位
 //   - "flex"：低优先级模式
-//   - 省略：normal 默认
+//   - 省略：normal 默认；策略中可用专用 "missing" 条件显式匹配
 //
 // 本策略复用 BetaPolicyAction*/BetaPolicyScope* 常量语义，只是匹配键从
 // anthropic-beta header 换成 body 的 service_tier 字段。
@@ -692,6 +692,7 @@ const (
 	OpenAIFastTierPriority  = "priority"  // 仅匹配 fast（priority）
 	OpenAIFastTierUltrafast = "ultrafast" // 仅匹配 ultrafast
 	OpenAIFastTierFlex      = "flex"      // 仅匹配 flex
+	OpenAIFastTierMissing   = "missing"   // 仅匹配省略 service_tier 的请求
 
 	// OpenAIFastPolicyActionForcePriority 会保留 service_tier 字段并强制写成
 	// priority，用于把 flex/auto/default/scale 等已识别 tier 收敛为 fast。
@@ -700,7 +701,7 @@ const (
 
 // OpenAIFastPolicyRule 单条 OpenAI fast/flex 策略规则
 type OpenAIFastPolicyRule struct {
-	ServiceTier          string   `json:"service_tier"`                     // "priority" | "ultrafast" | "flex" | "auto" | "default" | "scale" | "all"
+	ServiceTier          string   `json:"service_tier"`                     // "priority" | "ultrafast" | "flex" | "missing" | "all"
 	Action               string   `json:"action"`                           // "pass" | "filter" | "block" | "force_priority"
 	Scope                string   `json:"scope"`                            // "all" | "oauth" | "apikey" | "bedrock"
 	UserIDs              []int64  `json:"user_ids,omitempty"`               // 空=所有 Sub2API 用户；非空=仅指定 API Key 所属用户
diff --git a/frontend/src/api/admin/settings.ts b/frontend/src/api/admin/settings.ts
index 9404916394..4c8c06a7a3 100644
--- a/frontend/src/api/admin/settings.ts
+++ b/frontend/src/api/admin/settings.ts
@@ -1441,7 +1441,7 @@ export async function updateRectifierSettings(
  * Matches backend dto.OpenAIFastPolicyRule.
  */
 export interface OpenAIFastPolicyRule {
-  service_tier: "all" | "priority" | "flex" | "ultrafast";
+  service_tier: "all" | "priority" | "flex" | "ultrafast" | "missing";
   action: "pass" | "filter" | "block" | "force_priority";
   scope: "all" | "oauth" | "apikey" | "bedrock";
   user_ids?: number[];
diff --git a/frontend/src/i18n/__tests__/openaiFastPolicyLocales.spec.ts b/frontend/src/i18n/__tests__/openaiFastPolicyLocales.spec.ts
index 422db45776..cea1adfd1b 100644
--- a/frontend/src/i18n/__tests__/openaiFastPolicyLocales.spec.ts
+++ b/frontend/src/i18n/__tests__/openaiFastPolicyLocales.spec.ts
@@ -32,6 +32,7 @@ describe('OpenAI Fast/Flex policy locale keys', () => {
     expect(zh.admin.settings.openaiFastPolicy).toMatchObject({
       tierAll: '全部 tier 值',
       tierUltrafast: 'ultrafast',
+      tierMissing: '省略 tier',
       modelWhitelist: '目标模型',
       fallbackAction: '其他模型处理方式',
       summaryTargetModels: '目标模型',
@@ -45,6 +46,7 @@ describe('OpenAI Fast/Flex policy locale keys', () => {
     expect(en.admin.settings.openaiFastPolicy).toMatchObject({
       tierAll: 'All tier values',
       tierUltrafast: 'ultrafast',
+      tierMissing: 'Omitted tier',
       modelWhitelist: 'Target models',
       fallbackAction: 'Other models action',
       summaryTargetModels: 'Target models',
diff --git a/frontend/src/i18n/locales/en/admin/settings.ts b/frontend/src/i18n/locales/en/admin/settings.ts
index 57c78d3cec..99e82fb12b 100644
--- a/frontend/src/i18n/locales/en/admin/settings.ts
+++ b/frontend/src/i18n/locales/en/admin/settings.ts
@@ -1100,7 +1100,7 @@ export default {
       },
       openaiFastPolicy: {
         title: 'OpenAI Fast/Flex Policy',
-        description: 'Intercept, filter, or pass OpenAI fast(priority), ultrafast, or flex requests based on the request body service_tier field. Applies to the OpenAI gateway only.',
+        description: 'Intercept, filter, or pass OpenAI fast(priority), ultrafast, or flex requests based on the request body service_tier field. Applies to the OpenAI gateway only. "All tier values" includes explicitly sent tiers only.',
         empty: 'No rules configured. Click the button below to add one.',
         ruleHeader: 'Rule #{index}',
         removeRule: 'Remove rule',
@@ -1108,6 +1108,7 @@ export default {
         saveHint: 'Saved together with system settings (click the global Save button at the bottom of the page).',
         serviceTier: 'service_tier match',
         tierAll: 'All tier values',
+        tierMissing: 'Omitted tier',
         tierPriority: 'priority (fast)',
         tierUltrafast: 'ultrafast',
         tierFlex: 'flex',
diff --git a/frontend/src/i18n/locales/zh/admin/settings.ts b/frontend/src/i18n/locales/zh/admin/settings.ts
index 463f4f671f..df178cb67d 100644
--- a/frontend/src/i18n/locales/zh/admin/settings.ts
+++ b/frontend/src/i18n/locales/zh/admin/settings.ts
@@ -1094,7 +1094,7 @@ export default {
       },
       openaiFastPolicy: {
         title: 'OpenAI Fast/Flex 策略',
-        description: '基于请求体 service_tier 字段拦截/过滤/透传 OpenAI fast(priority)、ultrafast 与 flex 请求；仅作用于 OpenAI 网关。',
+        description: '基于请求体 service_tier 字段拦截/过滤/透传 OpenAI fast(priority)、ultrafast 与 flex 请求；仅作用于 OpenAI 网关。“全部 tier 值”仅包含显式传入的 tier。',
         empty: '尚未配置任何规则。点击下方按钮新增。',
         ruleHeader: '规则 #{index}',
         removeRule: '删除规则',
@@ -1102,6 +1102,7 @@ export default {
         saveHint: '保存时随系统设置一起提交（点击页面底部「保存」按钮）。',
         serviceTier: 'service_tier 匹配',
         tierAll: '全部 tier 值',
+        tierMissing: '省略 tier',
         tierPriority: 'priority（fast）',
         tierUltrafast: 'ultrafast',
         tierFlex: 'flex',
diff --git a/frontend/src/views/admin/SettingsView.vue b/frontend/src/views/admin/SettingsView.vue
index 234d2c3404..c25b06eb3b 100644
--- a/frontend/src/views/admin/SettingsView.vue
+++ b/frontend/src/views/admin/SettingsView.vue
@@ -1184,6 +1184,7 @@
                           | 'all'
                           | 'priority'
                           | 'flex'
+                          | 'missing'
                       "
                       :options="openaiFastPolicyTierOptions"
                     />
@@ -12179,6 +12180,7 @@ const openaiFastPolicyTierOptions = computed(() => [
     label: t("admin.settings.openaiFastPolicy.tierUltrafast"),
   },
   { value: "flex", label: t("admin.settings.openaiFastPolicy.tierFlex") },
+  { value: "missing", label: t("admin.settings.openaiFastPolicy.tierMissing") },
 ]);
 
 const openaiFastPolicyActionOptions = computed(() => [