diff --git a/backend/internal/pkg/claude/constants.go b/backend/internal/pkg/claude/constants.go
index 3c9f5089..3c028cf1 100644
--- a/backend/internal/pkg/claude/constants.go
+++ b/backend/internal/pkg/claude/constants.go
@@ -8,16 +8,49 @@ import (
 )
 
 // Claude Code 客户端相关常量
+//
+// 反编译 @anthropic-ai/claude-code 2.1.145（Bun 1.3.14 打包）确认的真实指纹：
+//   VERSION       = 2.1.145
+//   SDK 内嵌      = @anthropic-ai/sdk@0.94.0
+//   BUILD_TIME    = 2026-05-19T01:36:35Z
+//   GIT_SHA       = daa4c3755d45ab0cf97bb41db8c03bd2dfd2ff5f
+//   X-Stainless-Runtime         = "node"          (Bun 经 globalThis.process 检测为 node)
+//   X-Stainless-Runtime-Version = globalThis.process.version (Bun Node-compat 字符串)
 
-// DefaultCLIVersion 是当前模拟的 Claude CLI 版本
+// ClaudeCodeBundle 描述当前 sub2api 对外伪装的 Claude Code CLI 构建快照。
+// 每次升级目标 CLI 版本时，更新 DefaultBundle 即可。
+type ClaudeCodeBundle struct {
+	CLIVersion     string
+	SDKVersion     string
+	BuildDate      string
+	GitSHA         string
+	RuntimeVersion string
+	DefaultOS      string
+	DefaultArch    string
+}
+
+// DefaultBundle 是 sub2api 对外伪装的 Claude Code CLI 构建快照。
+// 当 Claude Code 发新版且抓包确认指纹变化时，更新此处常量并同步测试断言。
+var DefaultBundle = ClaudeCodeBundle{
+	CLIVersion:     "2.1.145",
+	SDKVersion:     "0.94.0",
+	BuildDate:      "2026-05-19T01:36:35Z",
+	GitSHA:         "daa4c3755d45ab0cf97bb41db8c03bd2dfd2ff5f",
+	RuntimeVersion: "v24.3.0",
+	DefaultOS:      "MacOS",
+	DefaultArch:    "arm64",
+}
+
+// 所有 Default* 变量从 DefaultBundle 派生。请勿在此包外直接修改它们，
+// 改用 ApplyFingerprintOverrides 保持 bundle 与派生变量一致。
 var (
-	DefaultCLIVersion              = "2.1.104"
+	DefaultCLIVersion              = DefaultBundle.CLIVersion
 	DefaultStainlessLang           = "js"
-	DefaultStainlessPackageVersion = "0.81.0"
-	DefaultStainlessOS             = "MacOS"
-	DefaultStainlessArch           = "arm64"
+	DefaultStainlessPackageVersion = DefaultBundle.SDKVersion
+	DefaultStainlessOS             = DefaultBundle.DefaultOS
+	DefaultStainlessArch           = DefaultBundle.DefaultArch
 	DefaultStainlessRuntime        = "node"
-	DefaultStainlessRuntimeVersion = "v24.3.0"
+	DefaultStainlessRuntimeVersion = DefaultBundle.RuntimeVersion
 	DefaultStainlessRetryCount     = "0"
 	DefaultStainlessTimeout        = "600"
 	DefaultXApp                    = "cli"
@@ -211,30 +244,46 @@ func AttributionHeaderDisabled() bool {
 
 // Beta header 常量
 //
-// 这里的常量对齐真实 Claude Code CLI 的最新流量（截至 2026-04）。
-// 选型参考：与 Parrot (src/transform/cc_mimicry.py) 的 BETAS 保持一致，
+// 这里的常量对齐真实 Claude Code CLI 的最新流量（截至 2026-05，2.1.145 抓包）。
+// 选型来源：反编译 2.1.145 binary 的内部 capability 注册表（JM("name", "beta-X-Y-Z")）。
 // 原因：Anthropic 上游会基于 anthropic-beta 的完整集合判定请求来源；
 // 缺少任何"官方 Claude Code 请求才会带"的 beta，都会被降级到第三方额度，
 // 对应报错：`Third-party apps now draw from your extra usage, not your plan limits.`
 const (
-	BetaOAuth                    = "oauth-2025-04-20"
-	BetaClaudeCode               = "claude-code-20250219"
-	BetaInterleavedThinking      = "interleaved-thinking-2025-05-14"
-	BetaFineGrainedToolStreaming = "fine-grained-tool-streaming-2025-05-14"
-	BetaTokenCounting            = "token-counting-2024-11-01"
-	BetaContext1M                = "context-1m-2025-08-07"
-	BetaFastMode                 = "fast-mode-2026-02-01"
-	// 新增（对齐官方 CLI 2.1.9x 以来的流量）
+	BetaOAuth               = "oauth-2025-04-20"
+	BetaClaudeCode          = "claude-code-20250219"
+	BetaInterleavedThinking = "interleaved-thinking-2025-05-14"
+	BetaTokenCounting       = "token-counting-2024-11-01"
+	BetaContext1M           = "context-1m-2025-08-07"
+	BetaFastMode            = "fast-mode-2026-02-01"
 	BetaPromptCachingScope  = "prompt-caching-scope-2026-01-05"
 	BetaEffort              = "effort-2025-11-24"
 	BetaRedactThinking      = "redact-thinking-2026-02-12"
 	BetaContextManagement   = "context-management-2025-06-27"
 	BetaExtendedCacheTTL    = "extended-cache-ttl-2025-04-11"
 	BetaTaskBudgets         = "task-budgets-2026-03-13"
-	BetaTokenEfficientTools = "token-efficient-tools-2026-03-28"
 	BetaStructuredOutputs   = "structured-outputs-2025-12-15"
 	BetaAdvisor             = "advisor-tool-2026-03-01"
 	BetaWebSearch           = "web-search-2025-03-05"
+
+	// 2026-05 已 GA 的 beta，保留常量供 client 显式传入时 merge 使用，
+	// 但 sub2api 默认不再注入到 OAuth/API-key mimic header 中。
+	BetaFineGrainedToolStreaming = "fine-grained-tool-streaming-2025-05-14"
+	BetaTokenEfficientTools      = "token-efficient-tools-2025-02-19" // 修正原 2026-03-28 错日期
+
+	// 2.1.145 反编译新增（对齐官方 CLI 2.1.1xx 以来的流量）
+	BetaAdvancedToolUse       = "advanced-tool-use-2025-11-20"
+	BetaToolSearchTool        = "tool-search-tool-2025-10-19"
+	BetaMCPServers            = "mcp-servers-2025-12-04"
+	BetaMCPClient             = "mcp-client-2025-11-20"
+	BetaMidConversationSystem = "mid-conversation-system-2026-04-07"
+	BetaAFKMode               = "afk-mode-2026-01-31"
+	BetaCacheDiagnosis        = "cache-diagnosis-2026-04-07"
+	BetaContextHint           = "context-hint-2026-04-09"
+	BetaEnvironments          = "environments-2025-11-01"
+	BetaManagedAgents         = "managed-agents-2026-04-01"
+	BetaSkills                = "skills-2025-10-02"
+	BetaCompact               = "compact-2026-01-12"
 )
 
 // DroppedBetas 是转发时需要从 anthropic-beta header 中移除的 beta token 列表。
@@ -243,7 +292,8 @@ var DroppedBetas = []string{}
 
 // DefaultBetaHeader Claude Code 客户端默认的 anthropic-beta header（OAuth 账号，不含 context-1m）
 // 使用 GetOAuthBetaHeader(modelID) 获取含 context-1m 的 model-aware 版本。
-const DefaultBetaHeader = BetaClaudeCode + "," + BetaOAuth + "," + BetaInterleavedThinking + "," + BetaFineGrainedToolStreaming + "," + BetaRedactThinking + "," + BetaContextManagement + "," + BetaPromptCachingScope + "," + BetaEffort
+// 已移除 GA 的 BetaFineGrainedToolStreaming。
+const DefaultBetaHeader = BetaClaudeCode + "," + BetaOAuth + "," + BetaInterleavedThinking + "," + BetaRedactThinking + "," + BetaContextManagement + "," + BetaPromptCachingScope + "," + BetaEffort
 
 // MessageBetaHeaderNoTools /v1/messages 在无工具时的 beta header（OAuth，不含 context-1m）
 //
@@ -264,13 +314,14 @@ const HaikuBetaHeader = BetaOAuth + "," + BetaInterleavedThinking + "," + BetaEf
 
 // APIKeyBetaHeader API-key 账号使用的 anthropic-beta header（不含 oauth / context-1m）
 // 使用 GetAPIKeyBetaHeader(modelID) 获取含 context-1m 的 model-aware 版本。
-const APIKeyBetaHeader = BetaClaudeCode + "," + BetaInterleavedThinking + "," + BetaFineGrainedToolStreaming + "," + BetaEffort + "," + BetaPromptCachingScope
+// 已移除 GA 的 BetaFineGrainedToolStreaming。
+const APIKeyBetaHeader = BetaClaudeCode + "," + BetaInterleavedThinking + "," + BetaEffort + "," + BetaPromptCachingScope
 
 // APIKeyHaikuBetaHeader Haiku 模型在 API-key 账号下使用的 anthropic-beta header（不含 oauth / claude-code）
 const APIKeyHaikuBetaHeader = BetaInterleavedThinking + "," + BetaEffort
 
 // ModelSupports1M 判断模型是否支持 1M context window。
-// 与 claude-code-2.1.104 bundle 中 modelSupports1M 逻辑保持一致：
+// 与 Claude Code CLI bundle 中 modelSupports1M 逻辑保持一致（截至 2.1.145 反编译）：
 //
 //	claude-sonnet-4 系列 和 claude-opus-4-6 支持 1M context。
 func ModelSupports1M(modelID string) bool {
@@ -280,21 +331,23 @@ func ModelSupports1M(modelID string) bool {
 
 // GetOAuthBetaHeader 返回 OAuth 账号的 beta header。
 // 仅当模型支持 1M context 时才包含 context-1m-2025-08-07。
+// 已移除 GA 的 BetaFineGrainedToolStreaming。
 func GetOAuthBetaHeader(modelID string) string {
 	if ModelSupports1M(modelID) {
-		return BetaClaudeCode + "," + BetaOAuth + "," + BetaInterleavedThinking + "," + BetaFineGrainedToolStreaming + "," + BetaContext1M + "," + BetaRedactThinking + "," + BetaContextManagement + "," + BetaPromptCachingScope + "," + BetaEffort
+		return BetaClaudeCode + "," + BetaOAuth + "," + BetaInterleavedThinking + "," + BetaContext1M + "," + BetaRedactThinking + "," + BetaContextManagement + "," + BetaPromptCachingScope + "," + BetaEffort
 	}
 	return DefaultBetaHeader
 }
 
 // GetAPIKeyBetaHeader 返回 API-key 账号的 beta header。
 // 仅当模型支持 1M context 时才包含 context-1m-2025-08-07。
+// 已移除 GA 的 BetaFineGrainedToolStreaming。
 func GetAPIKeyBetaHeader(modelID string) string {
 	if strings.Contains(strings.ToLower(modelID), "haiku") {
 		return APIKeyHaikuBetaHeader
 	}
 	if ModelSupports1M(modelID) {
-		return BetaClaudeCode + "," + BetaInterleavedThinking + "," + BetaFineGrainedToolStreaming + "," + BetaContext1M + "," + BetaEffort + "," + BetaPromptCachingScope
+		return BetaClaudeCode + "," + BetaInterleavedThinking + "," + BetaContext1M + "," + BetaEffort + "," + BetaPromptCachingScope
 	}
 	return APIKeyBetaHeader
 }
@@ -307,45 +360,62 @@ const DefaultCacheControlTTL = "5m"
 // CLICurrentVersion 是 sub2api 当前对外伪装的 Claude Code CLI 版本号（三段 semver）。
 // 用于 billing attribution block 中的 cc_version=X.Y.Z.{fp} 前缀以及 fingerprint 计算。
 // 必须与 DefaultHeaders["User-Agent"] 中的版本号严格一致；不一致会被 Anthropic 判第三方。
-const CLICurrentVersion = "2.1.92"
+//
+// 从 var 改为派生自 DefaultBundle.CLIVersion，避免硬编码漂移。
+var CLICurrentVersion = DefaultBundle.CLIVersion
 
-// FullClaudeCodeMimicryBetas 返回最"像"真实 Claude Code CLI 的完整 beta 列表，
+// FullClaudeCodeMimicryBetas 返回最"像"真实 Claude Code CLI 2.1.145 的完整 beta 列表，
 // 用于 OAuth 账号伪装成 Claude Code 时使用。
-// 顺序与真实 CLI 抓包一致。
+// 顺序基于反编译 2.1.145 binary 中的 capability 注册顺序，与真实 CLI 抓包匹配。
 //
 // 使用建议：
 //   - OAuth 账号 + 非 haiku：追加这整份列表，再按需保留 client 带来的 beta。
 //   - OAuth 账号 + haiku：Anthropic 对 haiku 不做 third-party 判定，使用 HaikuBetaHeader 即可。
 //   - API-key 账号：不要使用本函数，参见 APIKeyBetaHeader。
 //   - 不默认加入 redact-thinking，避免上游抹除 thinking 内容；客户端显式传入时由合并逻辑保留。
+//   - 不加入已 GA 的 BetaFineGrainedToolStreaming / BetaTokenEfficientTools；
+//     这些常量仍保留供客户端显式 merge 使用。
 func FullClaudeCodeMimicryBetas() []string {
 	return []string{
+		// 核心身份 token
 		BetaClaudeCode,
 		BetaOAuth,
+		// 思考与工具
 		BetaInterleavedThinking,
+		BetaAdvancedToolUse,
+		BetaToolSearchTool,
+		// MCP
+		BetaMCPClient,
+		BetaMCPServers,
+		// 上下文与缓存
 		BetaPromptCachingScope,
-		BetaEffort,
-		BetaContextManagement,
 		BetaExtendedCacheTTL,
+		BetaContextManagement,
+		BetaContextHint,
+		BetaCacheDiagnosis,
+		// 系统提示与会话
+		BetaMidConversationSystem,
+		BetaCompact,
+		// 工作流
+		BetaEffort,
+		BetaTaskBudgets,
+		BetaAFKMode,
+		// 高级特性
+		BetaSkills,
+		BetaManagedAgents,
+		BetaEnvironments,
+		BetaAdvisor,
 	}
 }
 
 // DefaultHeaders 是 Claude Code 客户端默认请求头。
-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.
-	// 版本参考：对齐 Parrot (src/transform/cc_mimicry.py:49) 的 CLI_USER_AGENT。
-	"User-Agent":                                "claude-cli/2.1.92 (external, cli)",
-	"X-Stainless-Lang":                          "js",
-	"X-Stainless-Package-Version":               "0.70.0",
-	"X-Stainless-OS":                            "Linux",
-	"X-Stainless-Arch":                          "arm64",
-	"X-Stainless-Runtime":                       "node",
-	"X-Stainless-Runtime-Version":               "v24.13.0",
-	"X-Stainless-Retry-Count":                   "0",
-	"X-Stainless-Timeout":                       "600",
-	"X-App":                                     "cli",
-	"Anthropic-Dangerous-Direct-Browser-Access": "true",
+//
+// 由 init() 在包加载时从 DefaultBundle 派生构造，避免与 DefaultBundle 漂移。
+// 注：通过 ApplyFingerprintOverrides 更新指纹后，本变量会被重新构造。
+var DefaultHeaders map[string]string
+
+func init() {
+	DefaultHeaders = buildDefaultHeaders(DefaultDeviceProfile())
 }
 
 // Model 表示一个 Claude 模型
@@ -444,22 +514,36 @@ func DenormalizeModelID(id string) string {
 	return id
 }
 
-// ApplyFingerprintOverrides 用配置覆盖默认指纹值（每个实例可设不同值）
+// ApplyFingerprintOverrides 用配置覆盖默认指纹值（每个实例可设不同值）。
+//
+// 同步更新 DefaultBundle 与所有派生变量、DefaultHeaders、CLICurrentVersion，
+// 确保单一事实源。
 func ApplyFingerprintOverrides(cliVersion, pkgVersion, runtimeVersion, os_, arch string) {
 	if cliVersion != "" {
-		DefaultCLIVersion = strings.TrimSpace(cliVersion)
+		v := strings.TrimSpace(cliVersion)
+		DefaultBundle.CLIVersion = v
+		DefaultCLIVersion = v
+		CLICurrentVersion = v
 	}
 	if pkgVersion != "" {
-		DefaultStainlessPackageVersion = strings.TrimSpace(pkgVersion)
+		v := strings.TrimSpace(pkgVersion)
+		DefaultBundle.SDKVersion = v
+		DefaultStainlessPackageVersion = v
 	}
 	if runtimeVersion != "" {
-		DefaultStainlessRuntimeVersion = strings.TrimSpace(runtimeVersion)
+		v := strings.TrimSpace(runtimeVersion)
+		DefaultBundle.RuntimeVersion = v
+		DefaultStainlessRuntimeVersion = v
 	}
 	if os_ != "" {
-		DefaultStainlessOS = strings.TrimSpace(os_)
+		v := strings.TrimSpace(os_)
+		DefaultBundle.DefaultOS = v
+		DefaultStainlessOS = v
 	}
 	if arch != "" {
-		DefaultStainlessArch = strings.TrimSpace(arch)
+		v := strings.TrimSpace(arch)
+		DefaultBundle.DefaultArch = v
+		DefaultStainlessArch = v
 	}
 	DefaultHeaders = buildDefaultHeaders(DefaultDeviceProfile())
 }
diff --git a/backend/internal/pkg/claude/constants_test.go b/backend/internal/pkg/claude/constants_test.go
index b44ca96a..fcc15842 100644
--- a/backend/internal/pkg/claude/constants_test.go
+++ b/backend/internal/pkg/claude/constants_test.go
@@ -1,6 +1,65 @@
 package claude
 
-import "testing"
+import (
+	"strings"
+	"testing"
+)
+
+// TestDefaultBundleVersions verifies the active Claude Code bundle snapshot
+// matches the reverse-engineered 2.1.145 binary. Bump this when DefaultBundle
+// is upgraded to a newer CLI release.
+func TestDefaultBundleVersions(t *testing.T) {
+	if got := DefaultBundle.CLIVersion; got != "2.1.145" {
+		t.Fatalf("DefaultBundle.CLIVersion = %q, want %q", got, "2.1.145")
+	}
+	if got := DefaultBundle.SDKVersion; got != "0.94.0" {
+		t.Fatalf("DefaultBundle.SDKVersion = %q, want %q", got, "0.94.0")
+	}
+}
+
+// TestDefaultBundleDrivesLegacyExports ensures all legacy exported vars stay
+// in sync with DefaultBundle (single source of truth).
+func TestDefaultBundleDrivesLegacyExports(t *testing.T) {
+	if DefaultCLIVersion != DefaultBundle.CLIVersion {
+		t.Fatalf("DefaultCLIVersion = %q, want %q (from DefaultBundle)", DefaultCLIVersion, DefaultBundle.CLIVersion)
+	}
+	if DefaultStainlessPackageVersion != DefaultBundle.SDKVersion {
+		t.Fatalf("DefaultStainlessPackageVersion = %q, want %q (from DefaultBundle)", DefaultStainlessPackageVersion, DefaultBundle.SDKVersion)
+	}
+	if DefaultStainlessRuntimeVersion != DefaultBundle.RuntimeVersion {
+		t.Fatalf("DefaultStainlessRuntimeVersion = %q, want %q (from DefaultBundle)", DefaultStainlessRuntimeVersion, DefaultBundle.RuntimeVersion)
+	}
+	if DefaultStainlessOS != DefaultBundle.DefaultOS {
+		t.Fatalf("DefaultStainlessOS = %q, want %q (from DefaultBundle)", DefaultStainlessOS, DefaultBundle.DefaultOS)
+	}
+	if DefaultStainlessArch != DefaultBundle.DefaultArch {
+		t.Fatalf("DefaultStainlessArch = %q, want %q (from DefaultBundle)", DefaultStainlessArch, DefaultBundle.DefaultArch)
+	}
+	if CLICurrentVersion != DefaultBundle.CLIVersion {
+		t.Fatalf("CLICurrentVersion = %q, want %q (from DefaultBundle)", CLICurrentVersion, DefaultBundle.CLIVersion)
+	}
+}
+
+// TestDefaultHeadersDrivenByBundle ensures DefaultHeaders map carries the
+// values from DefaultBundle, not stale hard-coded literals.
+func TestDefaultHeadersDrivenByBundle(t *testing.T) {
+	if got := DefaultHeaders["X-Stainless-Package-Version"]; got != DefaultBundle.SDKVersion {
+		t.Fatalf("DefaultHeaders[X-Stainless-Package-Version] = %q, want %q", got, DefaultBundle.SDKVersion)
+	}
+	if got := DefaultHeaders["X-Stainless-Runtime-Version"]; got != DefaultBundle.RuntimeVersion {
+		t.Fatalf("DefaultHeaders[X-Stainless-Runtime-Version] = %q, want %q", got, DefaultBundle.RuntimeVersion)
+	}
+	if got := DefaultHeaders["X-Stainless-OS"]; got != DefaultBundle.DefaultOS {
+		t.Fatalf("DefaultHeaders[X-Stainless-OS] = %q, want %q", got, DefaultBundle.DefaultOS)
+	}
+	if got := DefaultHeaders["X-Stainless-Arch"]; got != DefaultBundle.DefaultArch {
+		t.Fatalf("DefaultHeaders[X-Stainless-Arch] = %q, want %q", got, DefaultBundle.DefaultArch)
+	}
+	ua := DefaultHeaders["User-Agent"]
+	if !strings.Contains(ua, "claude-cli/"+DefaultBundle.CLIVersion) {
+		t.Fatalf("DefaultHeaders[User-Agent] = %q, want substring %q", ua, "claude-cli/"+DefaultBundle.CLIVersion)
+	}
+}
 
 func TestApplyFingerprintOverridesUpdatesSharedDefaults(t *testing.T) {
 	t.Setenv("CLAUDE_CODE_ENTRYPOINT", "")
@@ -74,7 +133,7 @@ func TestDefaultUserAgentReflectsLocalRuntimeDescriptors(t *testing.T) {
 	t.Setenv("CLAUDE_CODE_WORKLOAD", "cron")
 
 	got := DefaultUserAgent()
-	want := "claude-cli/2.1.104 (external, sdk-cli, agent-sdk/0.0.77, client-app/cron-daemon, workload/cron)"
+	want := "claude-cli/2.1.145 (external, sdk-cli, agent-sdk/0.0.77, client-app/cron-daemon, workload/cron)"
 	if got != want {
 		t.Fatalf("DefaultUserAgent() = %q, want %q", got, want)
 	}
@@ -86,7 +145,7 @@ func TestDetailedCodeUserAgentReflectsEntrypointAndSDK(t *testing.T) {
 	t.Setenv("CLAUDE_AGENT_SDK_CLIENT_APP", "desktop")
 
 	got := DetailedCodeUserAgent()
-	want := "claude-code/2.1.104 (remote, agent-sdk/0.0.77, client-app/desktop)"
+	want := "claude-code/2.1.145 (remote, agent-sdk/0.0.77, client-app/desktop)"
 	if got != want {
 		t.Fatalf("DetailedCodeUserAgent() = %q, want %q", got, want)
 	}
diff --git a/backend/internal/pkg/claudemask/mask.go b/backend/internal/pkg/claudemask/mask.go
index db26bb82..218676a9 100644
--- a/backend/internal/pkg/claudemask/mask.go
+++ b/backend/internal/pkg/claudemask/mask.go
@@ -24,6 +24,9 @@ var SuspiciousHeaders = []string{
 }
 
 // RequiredNodeHeaders 是 Node.js Claude Code 客户端必须有的头
+//
+// 来源：反编译 Claude Code 2.1.145 binary，确认这些头在每个 /v1/messages
+// 与 /v1/messages/count_tokens 请求中都会被 SDK 强制设置。
 var RequiredNodeHeaders = map[string]bool{
 	"User-Agent":                  true,
 	"X-Stainless-Lang":            true,
@@ -33,6 +36,9 @@ var RequiredNodeHeaders = map[string]bool{
 	"X-Stainless-OS":              true,
 	"X-Stainless-Arch":            true,
 	"anthropic-version":           true,
+	// 2.1.145 强制：SDK 内 `"X-Claude-Code-Session-Id":y_()`，
+	// 上游用其识别会话；缺失会被判第三方。
+	"X-Claude-Code-Session-Id": true,
 }
 
 // ValidateNodeEmulation 验证请求是否正确伪装为 Node.js 客户端
diff --git a/backend/internal/pkg/claudemask/mask_test.go b/backend/internal/pkg/claudemask/mask_test.go
index 442428b6..acc573f9 100644
--- a/backend/internal/pkg/claudemask/mask_test.go
+++ b/backend/internal/pkg/claudemask/mask_test.go
@@ -19,6 +19,8 @@ func TestValidateNodeEmulation_ValidRequest(t *testing.T) {
 	req.Header.Set("X-Stainless-OS", claude.DefaultStainlessOS)
 	req.Header.Set("X-Stainless-Arch", claude.DefaultStainlessArch)
 	req.Header.Set("anthropic-version", claude.DefaultAnthropicVersion)
+	// 2.1.145 强制：X-Claude-Code-Session-Id (UUID)
+	req.Header.Set("X-Claude-Code-Session-Id", "01970000-0000-7000-8000-000000000001")
 
 	isValid, errors := ValidateNodeEmulation(req)
 
@@ -44,8 +46,39 @@ func TestValidateNodeEmulation_MissingHeaders(t *testing.T) {
 	if len(errors) == 0 {
 		t.Error("expected validation errors")
 	}
-	if len(errors) < 7 {
-		t.Errorf("expected at least 7 missing headers, got %d errors", len(errors))
+	if len(errors) < 8 {
+		t.Errorf("expected at least 8 missing headers, got %d errors", len(errors))
+	}
+}
+
+// TestValidateNodeEmulation_MissingSessionID 验证 X-Claude-Code-Session-Id
+// 是强制头：缺失则验证失败。
+func TestValidateNodeEmulation_MissingSessionID(t *testing.T) {
+	req, _ := http.NewRequest("POST", "https://api.anthropic.com/v1/messages", nil)
+
+	// 设置所有 Stainless 头，但缺 session-id
+	req.Header.Set("User-Agent", claude.DefaultUserAgent())
+	req.Header.Set("X-Stainless-Lang", claude.DefaultStainlessLang)
+	req.Header.Set("X-Stainless-Runtime", claude.DefaultStainlessRuntime)
+	req.Header.Set("X-Stainless-Runtime-Version", claude.DefaultStainlessRuntimeVersion)
+	req.Header.Set("X-Stainless-Package-Version", claude.DefaultStainlessPackageVersion)
+	req.Header.Set("X-Stainless-OS", claude.DefaultStainlessOS)
+	req.Header.Set("X-Stainless-Arch", claude.DefaultStainlessArch)
+	req.Header.Set("anthropic-version", claude.DefaultAnthropicVersion)
+
+	isValid, errs := ValidateNodeEmulation(req)
+	if isValid {
+		t.Fatal("expected invalid due to missing X-Claude-Code-Session-Id")
+	}
+	foundSessionErr := false
+	for _, e := range errs {
+		if e == "missing required header: X-Claude-Code-Session-Id" {
+			foundSessionErr = true
+			break
+		}
+	}
+	if !foundSessionErr {
+		t.Fatalf("expected X-Claude-Code-Session-Id error, got: %v", errs)
 	}
 }
 
@@ -145,6 +178,8 @@ func TestValidateAndClean(t *testing.T) {
 	req.Header.Set("X-Stainless-OS", claude.DefaultStainlessOS)
 	req.Header.Set("X-Stainless-Arch", claude.DefaultStainlessArch)
 	req.Header.Set("anthropic-version", claude.DefaultAnthropicVersion)
+	// 2.1.145 强制：X-Claude-Code-Session-Id
+	req.Header.Set("X-Claude-Code-Session-Id", "01970000-0000-7000-8000-000000000002")
 
 	isValid, errors := ValidateAndClean(req)
 
diff --git a/backend/internal/service/claude_code_session_id.go b/backend/internal/service/claude_code_session_id.go
new file mode 100644
index 00000000..f087c004
--- /dev/null
+++ b/backend/internal/service/claude_code_session_id.go
@@ -0,0 +1,73 @@
+package service
+
+import (
+	"net/http"
+
+	"github.com/google/uuid"
+	"github.com/tidwall/gjson"
+)
+
+// ensureClaudeCodeSessionID 确保 X-Claude-Code-Session-Id header 被合理填充。
+//
+// 真实 Claude Code 2.1.145 CLI 在 SDK 内会始终设置 X-Claude-Code-Session-Id 为
+// 当前 CLI 会话的 UUID（源码：`"X-Claude-Code-Session-Id":y_()`）。上游若发现
+// 该头缺失，可能将请求识别为非官方 Claude Code 第三方调用。
+//
+// 行为按 tokenType / mimicClaudeCode 分两条路径：
+//
+//	OAuth mimic 路径 (tokenType == "oauth" && mimicClaudeCode):
+//	  1. body 中 metadata.user_id 派生的 SessionID 是合法 UUID → canonicalize 写入
+//	  2. 请求 header 中已有合法 UUID → canonicalize 保留
+//	  3. 否则 → 兜底生成 UUID
+//
+//	API key 透传 / 非 mimic 路径:
+//	  - 不从 body 合成 header（避免污染客户端原始语义）
+//	  - 但若客户端在 header 中传入了 X-Claude-Code-Session-Id：
+//	      合法 UUID → canonicalize 保留
+//	      非法值     → 删除（不向上游转发恶意值，符合 UUID 校验承诺）
+//	  - 不兜底生成
+//
+// 安全说明：metadata.user_id 由客户端控制，ParseMetadataUserID 的正则仅约束字符集，
+// 不保证 UUID 结构。因此所有写入 header 的 session id 都必须经 uuid.Parse 校验。
+func ensureClaudeCodeSessionID(req *http.Request, body []byte, tokenType string, mimicClaudeCode bool) {
+	if req == nil {
+		return
+	}
+	if req.Header == nil {
+		req.Header = make(http.Header)
+	}
+
+	isOAuthMimic := tokenType == "oauth" && mimicClaudeCode
+
+	// OAuth mimic 路径：从 metadata 派生（仅在 mimic 场景写 header）。
+	if isOAuthMimic {
+		if uid := gjson.GetBytes(body, "metadata.user_id").String(); uid != "" {
+			if parsed := ParseMetadataUserID(uid); parsed != nil {
+				if id, err := uuid.Parse(parsed.SessionID); err == nil {
+					setHeaderRaw(req.Header, "X-Claude-Code-Session-Id", id.String())
+					return
+				}
+			}
+		}
+	}
+
+	// 处理客户端已传入的 header：合法 → canonicalize，非法 → 删除。
+	// 这条规则对所有路径生效，避免恶意非 UUID 值向上游透传。
+	if existing := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id"); existing != "" {
+		if id, err := uuid.Parse(existing); err == nil {
+			canonical := id.String()
+			if canonical != existing {
+				setHeaderRaw(req.Header, "X-Claude-Code-Session-Id", canonical)
+			}
+			return
+		}
+		// 非法 UUID：删除避免透传
+		req.Header.Del("X-Claude-Code-Session-Id")
+	}
+
+	// OAuth mimic 兜底生成（仅 mimic 场景；API key 不污染）。
+	// uuid.NewString() 走 crypto/rand。
+	if isOAuthMimic {
+		setHeaderRaw(req.Header, "X-Claude-Code-Session-Id", uuid.NewString())
+	}
+}
diff --git a/backend/internal/service/claude_code_session_id_test.go b/backend/internal/service/claude_code_session_id_test.go
new file mode 100644
index 00000000..d5c9023b
--- /dev/null
+++ b/backend/internal/service/claude_code_session_id_test.go
@@ -0,0 +1,200 @@
+package service
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/google/uuid"
+)
+
+const (
+	testValidUUID    = "01970000-0000-7000-8000-000000000001"
+	testValidUUIDAlt = "01970000-0000-7000-8000-000000000002"
+)
+
+func newReq(t *testing.T) *http.Request {
+	t.Helper()
+	req, err := http.NewRequest("POST", "https://api.anthropic.com/v1/messages", nil)
+	if err != nil {
+		t.Fatalf("NewRequest: %v", err)
+	}
+	return req
+}
+
+func TestEnsureClaudeCodeSessionID_NilRequest(t *testing.T) {
+	// Should not panic.
+	ensureClaudeCodeSessionID(nil, nil, "oauth", true)
+}
+
+func TestEnsureClaudeCodeSessionID_FromMetadataJSON(t *testing.T) {
+	req := newReq(t)
+	body := []byte(`{"metadata":{"user_id":"{\"device_id\":\"abc\",\"account_uuid\":\"\",\"session_id\":\"` + testValidUUID + `\"}"}}`)
+	ensureClaudeCodeSessionID(req, body, "oauth", true)
+
+	got := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id")
+	if got != testValidUUID {
+		t.Fatalf("session_id = %q, want %q", got, testValidUUID)
+	}
+}
+
+func TestEnsureClaudeCodeSessionID_FromMetadataLegacy(t *testing.T) {
+	req := newReq(t)
+	// legacy format: user_{64hex}_account_{uuid}_session_{uuid}
+	dev := "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef"
+	acc := "11111111-2222-3333-4444-555555555555"
+	uid := "user_" + dev + "_account_" + acc + "_session_" + testValidUUID
+	body := []byte(`{"metadata":{"user_id":"` + uid + `"}}`)
+	ensureClaudeCodeSessionID(req, body, "oauth", true)
+
+	got := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id")
+	if got != testValidUUID {
+		t.Fatalf("session_id = %q, want %q", got, testValidUUID)
+	}
+}
+
+// 安全测试：metadata.user_id 中的 session_id 不是合法 UUID 时，
+// 必须 fallback 到 OAuth UUID 兜底，而不是写入恶意值。
+func TestEnsureClaudeCodeSessionID_RejectsMalformedMetadataUUID(t *testing.T) {
+	req := newReq(t)
+	// session_id 字段是 36 字符但非 UUID 格式（凑数 hex+dash）
+	bogus := "abcdefab-0000-0000-0000-not-a-real-uuid"
+	body := []byte(`{"metadata":{"user_id":"{\"device_id\":\"abc\",\"account_uuid\":\"\",\"session_id\":\"` + bogus + `\"}"}}`)
+	ensureClaudeCodeSessionID(req, body, "oauth", true)
+
+	got := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id")
+	if got == bogus {
+		t.Fatalf("malformed metadata session_id was written verbatim: %q", got)
+	}
+	if got == "" {
+		t.Fatalf("expected OAuth mimic to fallback to UUID, got empty")
+	}
+	if _, err := uuid.Parse(got); err != nil {
+		t.Fatalf("fallback session_id is not a valid UUID: %q (err=%v)", got, err)
+	}
+}
+
+func TestEnsureClaudeCodeSessionID_PreservesExistingValidHeader(t *testing.T) {
+	req := newReq(t)
+	setHeaderRaw(req.Header, "X-Claude-Code-Session-Id", testValidUUID)
+	ensureClaudeCodeSessionID(req, nil, "oauth", true)
+
+	got := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id")
+	if got != testValidUUID {
+		t.Fatalf("session_id = %q, want preserved %q", got, testValidUUID)
+	}
+}
+
+func TestEnsureClaudeCodeSessionID_OverwritesInvalidHeader(t *testing.T) {
+	req := newReq(t)
+	setHeaderRaw(req.Header, "X-Claude-Code-Session-Id", "not-a-uuid")
+	ensureClaudeCodeSessionID(req, nil, "oauth", true)
+
+	got := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id")
+	if got == "not-a-uuid" {
+		t.Fatalf("invalid header was not overwritten: %q", got)
+	}
+	if _, err := uuid.Parse(got); err != nil {
+		t.Fatalf("fallback session_id is not a valid UUID: %q (err=%v)", got, err)
+	}
+}
+
+func TestEnsureClaudeCodeSessionID_OAuthMimicFallback(t *testing.T) {
+	req := newReq(t)
+	ensureClaudeCodeSessionID(req, nil, "oauth", true)
+
+	got := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id")
+	if got == "" {
+		t.Fatalf("expected OAuth mimic fallback to set X-Claude-Code-Session-Id")
+	}
+	if _, err := uuid.Parse(got); err != nil {
+		t.Fatalf("fallback session_id is not a valid UUID: %q (err=%v)", got, err)
+	}
+}
+
+// API key passthrough 路径必须不被污染：缺失 session-id 时不强制生成。
+func TestEnsureClaudeCodeSessionID_DoesNotPolluteAPIKey(t *testing.T) {
+	req := newReq(t)
+	ensureClaudeCodeSessionID(req, nil, "api_key", false)
+
+	got := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id")
+	if got != "" {
+		t.Fatalf("API key path should NOT auto-generate session-id, got %q", got)
+	}
+}
+
+// API key 路径即使 body 中有合法 metadata.user_id，也不应该派生 session-id 头。
+// 这是 fresh code review 发现的 C1 修复：保护客户端原始语义。
+func TestEnsureClaudeCodeSessionID_APIKeyIgnoresMetadata(t *testing.T) {
+	req := newReq(t)
+	// 客户端传入合法的 metadata.user_id，但 tokenType=api_key
+	body := []byte(`{"metadata":{"user_id":"{\"device_id\":\"abc\",\"account_uuid\":\"\",\"session_id\":\"` + testValidUUID + `\"}"}}`)
+	ensureClaudeCodeSessionID(req, body, "api_key", false)
+
+	got := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id")
+	if got != "" {
+		t.Fatalf("API key path must NOT derive session-id from metadata, got %q", got)
+	}
+}
+
+// OAuth 但非 mimic 模式也不应该从 metadata 派生 header。
+func TestEnsureClaudeCodeSessionID_OAuthNonMimicIgnoresMetadata(t *testing.T) {
+	req := newReq(t)
+	body := []byte(`{"metadata":{"user_id":"{\"device_id\":\"abc\",\"account_uuid\":\"\",\"session_id\":\"` + testValidUUID + `\"}"}}`)
+	ensureClaudeCodeSessionID(req, body, "oauth", false)
+
+	got := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id")
+	if got != "" {
+		t.Fatalf("Non-mimic OAuth must NOT derive session-id from metadata, got %q", got)
+	}
+}
+
+// API key 路径若客户端传入了非法 UUID header，必须删除避免向上游透传。
+// 这是 C2 修复：UUID 校验承诺要对所有路径生效。
+func TestEnsureClaudeCodeSessionID_APIKeyDeletesInvalidHeader(t *testing.T) {
+	req := newReq(t)
+	setHeaderRaw(req.Header, "X-Claude-Code-Session-Id", "not-a-uuid")
+	ensureClaudeCodeSessionID(req, nil, "api_key", false)
+
+	got := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id")
+	if got != "" {
+		t.Fatalf("API key path must delete invalid header, got %q", got)
+	}
+}
+
+// API key 路径若客户端传入了合法 UUID header，规范化保留（不删除）。
+func TestEnsureClaudeCodeSessionID_APIKeyPreservesValidHeader(t *testing.T) {
+	req := newReq(t)
+	setHeaderRaw(req.Header, "X-Claude-Code-Session-Id", testValidUUID)
+	ensureClaudeCodeSessionID(req, nil, "api_key", false)
+
+	got := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id")
+	if got != testValidUUID {
+		t.Fatalf("API key path must preserve valid client header, got %q want %q", got, testValidUUID)
+	}
+}
+
+// OAuth 但非 mimic 场景：保留客户端原始语义，不自动生成。
+func TestEnsureClaudeCodeSessionID_OAuthNonMimicDoesNotForce(t *testing.T) {
+	req := newReq(t)
+	ensureClaudeCodeSessionID(req, nil, "oauth", false)
+
+	got := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id")
+	if got != "" {
+		t.Fatalf("non-mimic OAuth should not auto-generate, got %q", got)
+	}
+}
+
+// 验证不同 UUID 输入会被规范化为 canonical 小写形式。
+func TestEnsureClaudeCodeSessionID_CanonicalForm(t *testing.T) {
+	req := newReq(t)
+	// 大写 UUID 输入
+	upper := "01970000-0000-7000-8000-ABCDEF000003"
+	setHeaderRaw(req.Header, "X-Claude-Code-Session-Id", upper)
+	ensureClaudeCodeSessionID(req, nil, "oauth", true)
+
+	got := getHeaderRaw(req.Header, "X-Claude-Code-Session-Id")
+	want := "01970000-0000-7000-8000-abcdef000003"
+	if got != want {
+		t.Fatalf("session_id = %q, want canonical %q", got, want)
+	}
+}
diff --git a/backend/internal/service/gateway_service.go b/backend/internal/service/gateway_service.go
index e25e6d82..5a00bbc7 100644
--- a/backend/internal/service/gateway_service.go
+++ b/backend/internal/service/gateway_service.go
@@ -6253,13 +6253,10 @@ func (s *GatewayService) buildUpstreamRequest(ctx context.Context, c *gin.Contex
 	}
 
 	// X-Claude-Code-Session-Id 头处理：
-	// 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)
-		}
-	}
+	// Claude Code 2.1.145 SDK 内强制设置该头（`"X-Claude-Code-Session-Id":y_()`）。
+	// 优先取 metadata.user_id 中的 sessionID；OAuth mimic 场景缺失时兜底 UUID，
+	// 避免上游基于该头缺失判定为第三方调用。
+	ensureClaudeCodeSessionID(req, body, tokenType, mimicClaudeCode)
 
 	// x-client-request-id: 真实 CLI 每个请求生成新 UUID（仅 1P）。
 	if getHeaderRaw(req.Header, "x-client-request-id") == "" && tokenType == "oauth" {
@@ -9462,13 +9459,9 @@ func (s *GatewayService) buildCountTokensRequest(ctx context.Context, c *gin.Con
 		}
 	}
 
-	// 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)
-		}
-	}
+	// X-Claude-Code-Session-Id 头处理（count_tokens 路径）：
+	// 与 messages 路径保持同样逻辑，OAuth mimic 场景缺失时兜底 UUID。
+	ensureClaudeCodeSessionID(req, body, tokenType, mimicClaudeCode)
 
 	// x-client-request-id（count_tokens 路径）
 	if getHeaderRaw(req.Header, "x-client-request-id") == "" && tokenType == "oauth" {