diff --git a/backend/internal/pkg/claude/constants.go b/backend/internal/pkg/claude/constants.go
index c9c015bb..95f44630 100644
--- a/backend/internal/pkg/claude/constants.go
+++ b/backend/internal/pkg/claude/constants.go
@@ -1,8 +1,24 @@
 // Package claude provides constants and helpers for Claude API integration.
 package claude
 
+import "strings"
+
 // Claude Code 客户端相关常量
 
+const (
+	DefaultCLIProductVersion       = "2.1.88"
+	DefaultUserType                = "external"
+	DefaultEntrypoint              = "cli"
+	DefaultStainlessLang           = "js"
+	DefaultStainlessPackageVersion = "0.74.0"
+	DefaultStainlessOS             = "MacOS"
+	DefaultStainlessArch           = "arm64"
+	DefaultStainlessRuntime        = "node"
+	DefaultStainlessRuntimeVersion = "v24.3.0"
+	DefaultCLIUserAgent            = "claude-cli/" + DefaultCLIProductVersion + " (" + DefaultUserType + ", " + DefaultEntrypoint + ")"
+	DefaultCodeUserAgent           = "claude-code/" + DefaultCLIProductVersion
+)
+
 // Beta header 常量
 const (
 	BetaOAuth                    = "oauth-2025-04-20"
@@ -52,19 +68,45 @@ const APIKeyHaikuBetaHeader = BetaInterleavedThinking
 var DefaultHeaders = map[string]string{
 	// Keep these in sync with recent Claude CLI traffic to reduce the chance
 	// that Claude Code-scoped OAuth credentials are rejected as "non-CLI" usage.
-	"User-Agent":                                "claude-cli/2.1.84 (external, cli)",
-	"X-Stainless-Lang":                          "js",
-	"X-Stainless-Package-Version":               "0.74.0",
-	"X-Stainless-OS":                            "MacOS",
-	"X-Stainless-Arch":                          "arm64",
-	"X-Stainless-Runtime":                       "node",
-	"X-Stainless-Runtime-Version":               "v24.3.0",
+	"User-Agent":                                DefaultCLIUserAgent,
+	"X-Stainless-Lang":                          DefaultStainlessLang,
+	"X-Stainless-Package-Version":               DefaultStainlessPackageVersion,
+	"X-Stainless-OS":                            DefaultStainlessOS,
+	"X-Stainless-Arch":                          DefaultStainlessArch,
+	"X-Stainless-Runtime":                       DefaultStainlessRuntime,
+	"X-Stainless-Runtime-Version":               DefaultStainlessRuntimeVersion,
 	"X-Stainless-Retry-Count":                   "0",
 	"X-Stainless-Timeout":                       "600",
 	"X-App":                                     "cli",
 	"Anthropic-Dangerous-Direct-Browser-Access": "true",
 }
 
+// BuildCLIUserAgent returns the current Claude Code API client user-agent.
+func BuildCLIUserAgent(version, userType, entrypoint string) string {
+	version = strings.TrimSpace(version)
+	if version == "" {
+		version = DefaultCLIProductVersion
+	}
+	userType = strings.TrimSpace(userType)
+	if userType == "" {
+		userType = DefaultUserType
+	}
+	entrypoint = strings.TrimSpace(entrypoint)
+	if entrypoint == "" {
+		entrypoint = DefaultEntrypoint
+	}
+	return "claude-cli/" + version + " (" + userType + ", " + entrypoint + ")"
+}
+
+// BuildCodeUserAgent returns the current Claude Code transport/helper user-agent.
+func BuildCodeUserAgent(version string) string {
+	version = strings.TrimSpace(version)
+	if version == "" {
+		version = DefaultCLIProductVersion
+	}
+	return "claude-code/" + version
+}
+
 // ApplyFingerprintOverrides 用配置覆盖默认指纹值（每个实例可设不同值）
 // cliVersion: Claude CLI 版本（如 "2.1.81"）
 // pkgVersion: SDK 版本（如 "0.80.0"）
@@ -73,7 +115,7 @@ var DefaultHeaders = map[string]string{
 // arch: 架构（如 "arm64"）
 func ApplyFingerprintOverrides(cliVersion, pkgVersion, runtimeVersion, os_, arch string) {
 	if cliVersion != "" {
-		DefaultHeaders["User-Agent"] = "claude-cli/" + cliVersion + " (external, cli)"
+		DefaultHeaders["User-Agent"] = BuildCLIUserAgent(cliVersion, "", "")
 	}
 	if pkgVersion != "" {
 		DefaultHeaders["X-Stainless-Package-Version"] = pkgVersion
diff --git a/backend/internal/repository/claude_usage_service.go b/backend/internal/repository/claude_usage_service.go
index b44adde2..15329507 100644
--- a/backend/internal/repository/claude_usage_service.go
+++ b/backend/internal/repository/claude_usage_service.go
@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"time"
 
+	"github.com/Wei-Shaw/sub2api/internal/pkg/claude"
 	infraerrors "github.com/Wei-Shaw/sub2api/internal/pkg/errors"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/httpclient"
 	"github.com/Wei-Shaw/sub2api/internal/service"
@@ -15,8 +16,8 @@ import (
 
 const defaultClaudeUsageURL = "https://api.anthropic.com/api/oauth/usage"
 
-// 默认 User-Agent，与用户抓包的请求一致
-const defaultUsageUserAgent = "claude-code/2.1.7"
+// 默认 User-Agent，与 Claude Code 2.1.88 的 helper/transport 请求保持一致。
+const defaultUsageUserAgent = claude.DefaultCodeUserAgent
 
 type claudeUsageService struct {
 	usageURL          string
diff --git a/backend/internal/service/claude_code_detection_test.go b/backend/internal/service/claude_code_detection_test.go
index ff7ad7f4..463aa60d 100644
--- a/backend/internal/service/claude_code_detection_test.go
+++ b/backend/internal/service/claude_code_detection_test.go
@@ -40,6 +40,7 @@ func TestValidate_ClaudeCLIUserAgent(t *testing.T) {
 		want bool
 	}{
 		{"标准版本号", "claude-cli/1.0.0", true},
+		{"官方 transport UA", "claude-code/2.1.88", true},
 		{"多位版本号", "claude-cli/12.34.56", true},
 		{"大写开头", "Claude-CLI/1.0.0", true},
 		{"非 claude-cli", "curl/7.64.1", false},
@@ -90,6 +91,19 @@ func TestValidate_MessagesPath_FullValid(t *testing.T) {
 	require.True(t, result, "完整有效请求应通过")
 }
 
+func TestValidate_MessagesPath_FullValid_ClaudeCodeUA(t *testing.T) {
+	v := newTestValidator()
+
+	req := httptest.NewRequest("POST", "/v1/messages", nil)
+	req.Header.Set("User-Agent", "claude-code/2.1.88")
+	req.Header.Set("X-App", "claude-code")
+	req.Header.Set("anthropic-beta", "max-tokens-3-5-sonnet-2024-07-15")
+	req.Header.Set("anthropic-version", "2023-06-01")
+
+	result := v.Validate(req, validClaudeCodeBody())
+	require.True(t, result, "官方 transport/helper UA 也应通过")
+}
+
 func TestValidate_MessagesPath_MissingHeaders(t *testing.T) {
 	v := newTestValidator()
 	body := validClaudeCodeBody()
diff --git a/backend/internal/service/claude_code_validator.go b/backend/internal/service/claude_code_validator.go
index 4e8ced67..a40ccb95 100644
--- a/backend/internal/service/claude_code_validator.go
+++ b/backend/internal/service/claude_code_validator.go
@@ -15,11 +15,13 @@ import (
 type ClaudeCodeValidator struct{}
 
 var (
-	// User-Agent 匹配: claude-cli/x.x.x (仅支持官方 CLI，大小写不敏感)
-	claudeCodeUAPattern = regexp.MustCompile(`(?i)^claude-cli/\d+\.\d+\.\d+`)
+	// User-Agent 匹配: 官方 Claude Code 目前存在两类产品前缀：
+	// 1. 主 Anthropic API 客户端: claude-cli/x.y.z (...)
+	// 2. transport / helper 请求: claude-code/x.y.z
+	claudeCodeUAPattern = regexp.MustCompile(`(?i)^claude-(?:cli|code)/\d+\.\d+\.\d+`)
 
 	// 带捕获组的版本提取正则
-	claudeCodeUAVersionPattern = regexp.MustCompile(`(?i)^claude-cli/(\d+\.\d+\.\d+)`)
+	claudeCodeUAVersionPattern = regexp.MustCompile(`(?i)^claude-(?:cli|code)/(\d+\.\d+\.\d+)`)
 
 	// System prompt 相似度阈值（默认 0.5，和 claude-relay-service 一致）
 	systemPromptThreshold = 0.5
@@ -55,7 +57,7 @@ func NewClaudeCodeValidator() *ClaudeCodeValidator {
 // Validate 验证请求是否来自 Claude Code CLI
 // 采用与 claude-relay-service 完全一致的验证策略：
 //
-//	Step 1: User-Agent 检查 (必需) - 必须是 claude-cli/x.x.x
+//	Step 1: User-Agent 检查 (必需) - 必须是官方 claude-cli/ 或 claude-code/ 前缀
 //	Step 2: 对于非 messages 路径，只要 UA 匹配就通过
 //	Step 3: 检查 max_tokens=1 + haiku 探测请求绕过（UA 已验证）
 //	Step 4: 对于 messages 路径，进行严格验证：
diff --git a/backend/internal/service/claude_code_validator_test.go b/backend/internal/service/claude_code_validator_test.go
index f87c56e8..fd7e26da 100644
--- a/backend/internal/service/claude_code_validator_test.go
+++ b/backend/internal/service/claude_code_validator_test.go
@@ -64,6 +64,7 @@ func TestExtractVersion(t *testing.T) {
 		want string
 	}{
 		{"claude-cli/2.1.22 (darwin; arm64)", "2.1.22"},
+		{"claude-code/2.1.88", "2.1.88"},
 		{"claude-cli/1.0.0", "1.0.0"},
 		{"Claude-CLI/3.10.5 (linux; x86_64)", "3.10.5"}, // 大小写不敏感
 		{"curl/8.0.0", ""},                              // 非 Claude CLI
diff --git a/backend/internal/service/gateway_anthropic_apikey_passthrough_test.go b/backend/internal/service/gateway_anthropic_apikey_passthrough_test.go
index 6e19db32..9b962455 100644
--- a/backend/internal/service/gateway_anthropic_apikey_passthrough_test.go
+++ b/backend/internal/service/gateway_anthropic_apikey_passthrough_test.go
@@ -689,6 +689,41 @@ func TestGatewayService_AnthropicOAuth_NotAffectedByAPIKeyPassthroughToggle(t *t
 	require.Contains(t, getHeaderRaw(req.Header, "anthropic-beta"), claude.BetaOAuth, "OAuth 链路仍应按原逻辑补齐 oauth beta")
 }
 
+func TestGatewayService_AnthropicOAuth_InjectsClaudeCodeSessionHeaderFromMetadata(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/messages", nil)
+
+	sessionID := "12345678-1234-1234-1234-123456789abc"
+	body, err := json.Marshal(map[string]any{
+		"model": "claude-3-7-sonnet-20250219",
+		"metadata": map[string]any{
+			"user_id": FormatMetadataUserID(
+				"d61f76d0730d2b920763648949bad5c79742155c27037fc77ac3f9805cb90169",
+				"",
+				sessionID,
+				claude.DefaultCLIProductVersion,
+			),
+		},
+	})
+	require.NoError(t, err)
+
+	svc := &GatewayService{
+		cfg: &config.Config{
+			Gateway: config.GatewayConfig{MaxLineSize: defaultMaxLineSize},
+		},
+	}
+	account := &Account{
+		Platform: PlatformAnthropic,
+		Type:     AccountTypeOAuth,
+	}
+
+	req, err := svc.buildUpstreamRequest(context.Background(), c, account, body, "oauth-token", "oauth", "claude-3-7-sonnet-20250219", false, false)
+	require.NoError(t, err)
+	require.Equal(t, sessionID, getHeaderRaw(req.Header, "X-Claude-Code-Session-Id"))
+}
+
 func TestGatewayService_AnthropicOAuth_ForwardPreservesBillingHeaderSystemBlock(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 
diff --git a/backend/internal/service/gateway_prompt_test.go b/backend/internal/service/gateway_prompt_test.go
index 356536b0..e52a1a81 100644
--- a/backend/internal/service/gateway_prompt_test.go
+++ b/backend/internal/service/gateway_prompt_test.go
@@ -21,6 +21,12 @@ func TestIsClaudeCodeClient(t *testing.T) {
 			metadataUserID: "session_123e4567-e89b-12d3-a456-426614174000",
 			want:           true,
 		},
+		{
+			name:           "Claude Code helper client",
+			userAgent:      "claude-code/2.1.88",
+			metadataUserID: "session_123e4567-e89b-12d3-a456-426614174000",
+			want:           true,
+		},
 		{
 			name:           "Claude Code without version suffix",
 			userAgent:      "claude-cli/2.0.0",
diff --git a/backend/internal/service/gateway_service.go b/backend/internal/service/gateway_service.go
index b54f463b..107e5086 100644
--- a/backend/internal/service/gateway_service.go
+++ b/backend/internal/service/gateway_service.go
@@ -328,8 +328,8 @@ func isClaudeCodeCredentialScopeError(msg string) bool {
 // sseDataRe matches SSE data lines with optional whitespace after colon.
 // Some upstream APIs return non-standard "data:" without space (should be "data: ").
 var (
-	sseDataRe            = regexp.MustCompile(`^data:\s*`)
-	claudeCliUserAgentRe = regexp.MustCompile(`^claude-cli/\d+\.\d+\.\d+`)
+	sseDataRe             = regexp.MustCompile(`^data:\s*`)
+	claudeCodeUserAgentRe = regexp.MustCompile(`^claude-(?:cli|code)/\d+\.\d+\.\d+`)
 
 	// claudeCodePromptPrefixes 用于检测 Claude Code 系统提示词的前缀列表
 	// 支持多种变体：标准版、Agent SDK 版、Explore Agent 版、Compact 版等
@@ -3739,7 +3739,7 @@ func isClaudeCodeClient(userAgent string, metadataUserID string) bool {
 	if metadataUserID == "" {
 		return false
 	}
-	return claudeCliUserAgentRe.MatchString(userAgent)
+	return claudeCodeUserAgentRe.MatchString(userAgent)
 }
 
 func isClaudeCodeRequest(ctx context.Context, c *gin.Context, parsed *ParsedRequest) bool {
@@ -5758,12 +5758,11 @@ func (s *GatewayService) buildUpstreamRequest(ctx context.Context, c *gin.Contex
 		}
 	}
 
-	// 同步 X-Claude-Code-Session-Id 头：取 body 中已处理的 metadata.user_id 的 session_id 覆盖
-	if sessionHeader := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id"); sessionHeader != "" {
-		if uid := gjson.GetBytes(body, "metadata.user_id").String(); uid != "" {
-			if parsed := ParseMetadataUserID(uid); parsed != nil {
-				setHeaderRaw(req.Header, "X-Claude-Code-Session-Id", parsed.SessionID)
-			}
+	// Claude Code 主 API 客户端会始终发送 X-Claude-Code-Session-Id。
+	// 对于 mimic / 转发场景，只要 body 中 metadata.user_id 可解析，就主动注入并同步该头。
+	if uid := gjson.GetBytes(body, "metadata.user_id").String(); uid != "" {
+		if parsed := ParseMetadataUserID(uid); parsed != nil {
+			setHeaderRaw(req.Header, "X-Claude-Code-Session-Id", parsed.SessionID)
 		}
 	}
 
@@ -8486,12 +8485,11 @@ func (s *GatewayService) buildCountTokensRequest(ctx context.Context, c *gin.Con
 		}
 	}
 
-	// 同步 X-Claude-Code-Session-Id 头：取 body 中已处理的 metadata.user_id 的 session_id 覆盖
-	if sessionHeader := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id"); sessionHeader != "" {
-		if uid := gjson.GetBytes(body, "metadata.user_id").String(); uid != "" {
-			if parsed := ParseMetadataUserID(uid); parsed != nil {
-				setHeaderRaw(req.Header, "X-Claude-Code-Session-Id", parsed.SessionID)
-			}
+	// Claude Code 主 API 客户端会始终发送 X-Claude-Code-Session-Id。
+	// 对于 mimic / 转发场景，只要 body 中 metadata.user_id 可解析，就主动注入并同步该头。
+	if uid := gjson.GetBytes(body, "metadata.user_id").String(); uid != "" {
+		if parsed := ParseMetadataUserID(uid); parsed != nil {
+			setHeaderRaw(req.Header, "X-Claude-Code-Session-Id", parsed.SessionID)
 		}
 	}
 
diff --git a/backend/internal/service/identity_service.go b/backend/internal/service/identity_service.go
index c6a260a8..43351f73 100644
--- a/backend/internal/service/identity_service.go
+++ b/backend/internal/service/identity_service.go
@@ -13,6 +13,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/Wei-Shaw/sub2api/internal/pkg/claude"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/logger"
 	"github.com/tidwall/gjson"
 	"github.com/tidwall/sjson"
@@ -26,13 +27,13 @@ var (
 
 // 默认指纹值（当客户端未提供时使用）
 var defaultFingerprint = Fingerprint{
-	UserAgent:               "claude-cli/2.1.84 (external, cli)",
-	StainlessLang:           "js",
-	StainlessPackageVersion: "0.74.0",
-	StainlessOS:             "MacOS",
-	StainlessArch:           "arm64",
-	StainlessRuntime:        "node",
-	StainlessRuntimeVersion: "v24.3.0",
+	UserAgent:               claude.DefaultCLIUserAgent,
+	StainlessLang:           claude.DefaultStainlessLang,
+	StainlessPackageVersion: claude.DefaultStainlessPackageVersion,
+	StainlessOS:             claude.DefaultStainlessOS,
+	StainlessArch:           claude.DefaultStainlessArch,
+	StainlessRuntime:        claude.DefaultStainlessRuntime,
+	StainlessRuntimeVersion: claude.DefaultStainlessRuntimeVersion,
 }
 
 // Fingerprint represents account fingerprint data
diff --git a/backend/internal/service/identity_service_antigravity.go b/backend/internal/service/identity_service_antigravity.go
index e725a7fb..8416aff1 100644
--- a/backend/internal/service/identity_service_antigravity.go
+++ b/backend/internal/service/identity_service_antigravity.go
@@ -1,5 +1,7 @@
 package service
 
+import "github.com/Wei-Shaw/sub2api/internal/pkg/claude"
+
 // ==============================================================
 // antigravity — identity_service 扩展
 //
@@ -15,7 +17,7 @@ package service
 // 允许不同部署实例设置不同的 CLI/SDK 版本号，避免所有实例指纹相同
 func ApplyDefaultFingerprintOverrides(cliVersion, pkgVersion, runtimeVersion, os_, arch string) {
 	if cliVersion != "" {
-		defaultFingerprint.UserAgent = "claude-cli/" + cliVersion + " (external, cli)"
+		defaultFingerprint.UserAgent = claude.BuildCLIUserAgent(cliVersion, "", "")
 	}
 	if pkgVersion != "" {
 		defaultFingerprint.StainlessPackageVersion = pkgVersion