diff --git a/backend/cmd/server/wire_gen.go b/backend/cmd/server/wire_gen.go
index 2c1ac5b0..0e5182e0 100644
--- a/backend/cmd/server/wire_gen.go
+++ b/backend/cmd/server/wire_gen.go
@@ -12,6 +12,7 @@ import (
 	"github.com/Wei-Shaw/sub2api/internal/config"
 	"github.com/Wei-Shaw/sub2api/internal/handler"
 	"github.com/Wei-Shaw/sub2api/internal/handler/admin"
+	"github.com/Wei-Shaw/sub2api/internal/pkg/claude"
 	"github.com/Wei-Shaw/sub2api/internal/repository"
 	"github.com/Wei-Shaw/sub2api/internal/server"
 	"github.com/Wei-Shaw/sub2api/internal/server/middleware"
@@ -35,6 +36,10 @@ func initializeApplication(buildInfo handler.BuildInfo) (*Application, error) {
 	if err != nil {
 		return nil, err
 	}
+	// 应用实例级指纹覆盖（不同 sub2api 实例可设不同的默认版本号）
+	fpd := configConfig.Gateway.FingerprintDefaults
+	claude.ApplyFingerprintOverrides(fpd.ClaudeCLIVersion, fpd.StainlessPackageVersion, fpd.StainlessRuntimeVersion, fpd.StainlessOS, fpd.StainlessArch)
+	service.ApplyDefaultFingerprintOverrides(fpd.ClaudeCLIVersion, fpd.StainlessPackageVersion, fpd.StainlessRuntimeVersion, fpd.StainlessOS, fpd.StainlessArch)
 	client, err := repository.ProvideEnt(configConfig)
 	if err != nil {
 		return nil, err
@@ -167,7 +172,7 @@ func initializeApplication(buildInfo handler.BuildInfo) (*Application, error) {
 		return nil, err
 	}
 	billingService := service.NewBillingService(configConfig, pricingService)
-	identityService := service.NewIdentityService(identityCache)
+	identityService := service.NewIdentityServiceWithSalt(identityCache, configConfig.Gateway.InstanceSalt)
 	deferredService := service.ProvideDeferredService(accountRepository, timingWheelService)
 	claudeTokenProvider := service.ProvideClaudeTokenProvider(accountRepository, geminiTokenCache, oAuthService, oauthRefreshAPI)
 	digestSessionStore := service.NewDigestSessionStore()
diff --git a/backend/internal/config/config.go b/backend/internal/config/config.go
index ef9c81f7..02d9c37e 100644
--- a/backend/internal/config/config.go
+++ b/backend/internal/config/config.go
@@ -461,6 +461,18 @@ type GatewayConfig struct {
 	// 实现天然 JA3/JA4 指纹匹配（无需 uTLS 模拟）
 	NodeTLSProxy NodeTLSProxyConfig `mapstructure:"node_tls_proxy"`
 
+	// InstanceSalt: 实例级隔离盐值
+	// 用于 user_id 重写和 session hash 的种子混淆，
+	// 不同 sub2api 实例设置不同的 salt，确保相同输入产生不同输出。
+	// 为空时使用默认行为（无 salt），建议生产环境必须配置。
+	// 生成方法: openssl rand -hex 32
+	InstanceSalt string `mapstructure:"instance_salt"`
+
+	// FingerprintDefaults: 指纹默认值覆盖
+	// 允许每个实例配置不同的 Claude CLI 版本号，与其他 sub2api 实例区分。
+	// 为空时使用代码内置默认值。
+	FingerprintDefaults FingerprintDefaultsConfig `mapstructure:"fingerprint_defaults"`
+
 	// UsageRecord: 使用量记录异步队列配置（有界队列 + 固定 worker）
 	UsageRecord GatewayUsageRecordConfig `mapstructure:"usage_record"`
 
@@ -696,6 +708,23 @@ type NodeTLSProxyConfig struct {
 	ProxyHosts []string `mapstructure:"proxy_hosts"`
 }
 
+// FingerprintDefaultsConfig 指纹默认值配置
+// 允许每个 sub2api 实例设置不同的默认指纹值，与其他实例区分。
+// 所有字段为空时使用代码内置默认值。
+type FingerprintDefaultsConfig struct {
+	// ClaudeCLIVersion: Claude CLI 版本号（如 "2.1.81"），
+	// 最终 User-Agent 为 "claude-cli/{version} (external, cli)"
+	ClaudeCLIVersion string `mapstructure:"claude_cli_version"`
+	// StainlessPackageVersion: @anthropic-ai/sdk 版本（如 "0.80.0"）
+	StainlessPackageVersion string `mapstructure:"stainless_package_version"`
+	// StainlessRuntimeVersion: Node.js 版本（如 "v24.13.0"）
+	StainlessRuntimeVersion string `mapstructure:"stainless_runtime_version"`
+	// StainlessOS: 操作系统（如 "Linux", "Darwin"）
+	StainlessOS string `mapstructure:"stainless_os"`
+	// StainlessArch: 架构（如 "arm64", "x64"）
+	StainlessArch string `mapstructure:"stainless_arch"`
+}
+
 // GatewaySchedulingConfig accounts scheduling configuration.
 type GatewaySchedulingConfig struct {
 	// 粘性会话排队配置
diff --git a/backend/internal/pkg/claude/constants.go b/backend/internal/pkg/claude/constants.go
index 973bf79f..7fcbeee6 100644
--- a/backend/internal/pkg/claude/constants.go
+++ b/backend/internal/pkg/claude/constants.go
@@ -61,6 +61,30 @@ var DefaultHeaders = map[string]string{
 	"Anthropic-Dangerous-Direct-Browser-Access": "true",
 }
 
+// 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"）
+// runtimeVersion: Node.js 版本（如 "v24.13.0"）
+// os_: 操作系统（如 "Linux"）
+// arch: 架构（如 "arm64"）
+func ApplyFingerprintOverrides(cliVersion, pkgVersion, runtimeVersion, os_, arch string) {
+	if cliVersion != "" {
+		DefaultHeaders["User-Agent"] = "claude-cli/" + cliVersion + " (external, cli)"
+	}
+	if pkgVersion != "" {
+		DefaultHeaders["X-Stainless-Package-Version"] = pkgVersion
+	}
+	if runtimeVersion != "" {
+		DefaultHeaders["X-Stainless-Runtime-Version"] = runtimeVersion
+	}
+	if os_ != "" {
+		DefaultHeaders["X-Stainless-OS"] = os_
+	}
+	if arch != "" {
+		DefaultHeaders["X-Stainless-Arch"] = arch
+	}
+}
+
 // Model 表示一个 Claude 模型
 type Model struct {
 	ID          string `json:"id"`
diff --git a/backend/internal/service/identity_service.go b/backend/internal/service/identity_service.go
index a006cea9..7fc7beb3 100644
--- a/backend/internal/service/identity_service.go
+++ b/backend/internal/service/identity_service.go
@@ -35,6 +35,25 @@ var defaultFingerprint = Fingerprint{
 	StainlessRuntimeVersion: "v24.13.0",
 }
 
+// ApplyDefaultFingerprintOverrides 用配置覆盖 identity_service 的默认指纹
+func ApplyDefaultFingerprintOverrides(cliVersion, pkgVersion, runtimeVersion, os_, arch string) {
+	if cliVersion != "" {
+		defaultFingerprint.UserAgent = "claude-cli/" + cliVersion + " (external, cli)"
+	}
+	if pkgVersion != "" {
+		defaultFingerprint.StainlessPackageVersion = pkgVersion
+	}
+	if runtimeVersion != "" {
+		defaultFingerprint.StainlessRuntimeVersion = runtimeVersion
+	}
+	if os_ != "" {
+		defaultFingerprint.StainlessOS = os_
+	}
+	if arch != "" {
+		defaultFingerprint.StainlessArch = arch
+	}
+}
+
 // Fingerprint represents account fingerprint data
 type Fingerprint struct {
 	ClientID                string
@@ -63,7 +82,8 @@ type IdentityCache interface {
 
 // IdentityService 管理OAuth账号的请求身份指纹
 type IdentityService struct {
-	cache IdentityCache
+	cache        IdentityCache
+	instanceSalt string // 实例级隔离盐值，不同 sub2api 实例产生不同的 hash 输出
 }
 
 // NewIdentityService 创建新的IdentityService
@@ -71,6 +91,11 @@ func NewIdentityService(cache IdentityCache) *IdentityService {
 	return &IdentityService{cache: cache}
 }
 
+// NewIdentityServiceWithSalt 创建带实例盐值的 IdentityService
+func NewIdentityServiceWithSalt(cache IdentityCache, salt string) *IdentityService {
+	return &IdentityService{cache: cache, instanceSalt: salt}
+}
+
 // GetOrCreateFingerprint 获取或创建账号的指纹
 // 如果缓存存在，检测user-agent版本，新版本则更新
 // 如果缓存不存在，生成随机ClientID并从请求头创建指纹，然后缓存
@@ -241,8 +266,9 @@ func (s *IdentityService) RewriteUserID(body []byte, accountID int64, accountUUI
 
 	sessionTail := parsed.SessionID // 原始session UUID
 
-	// 生成新的session hash: SHA256(accountID::sessionTail) -> UUID格式
-	seed := fmt.Sprintf("%d::%s", accountID, sessionTail)
+	// 生成新的session hash: SHA256(salt::accountID::sessionTail) -> UUID格式
+	// instanceSalt 使不同 sub2api 实例对相同输入产生不同的 hash
+	seed := fmt.Sprintf("%s::%d::%s", s.instanceSalt, accountID, sessionTail)
 	newSessionHash := generateUUIDFromSeed(seed)
 
 	// 根据客户端版本选择输出格式
diff --git a/deploy/config.example.yaml b/deploy/config.example.yaml
index 738b622f..63df74a1 100644
--- a/deploy/config.example.yaml
+++ b/deploy/config.example.yaml
@@ -397,6 +397,24 @@ gateway:
     # Upstream target host / 上游目标主机
     upstream_host: "api.anthropic.com"
 
+  # Instance isolation salt / 实例隔离盐值
+  # IMPORTANT: Each sub2api deployment MUST set a unique salt to prevent
+  # cross-instance fingerprint correlation. Generate: openssl rand -hex 32
+  # 重要：每个 sub2api 实例必须设置唯一的 salt，防止不同实例之间的指纹关联。
+  # 生成方法: openssl rand -hex 32
+  instance_salt: ""
+
+  # Fingerprint defaults override / 指纹默认值覆盖
+  # Each instance can set different version numbers to differentiate from
+  # other sub2api deployments. Empty values use built-in defaults.
+  # 每个实例可设置不同的版本号，与其他 sub2api 部署区分。空值使用内置默认值。
+  fingerprint_defaults:
+    # claude_cli_version: "2.1.81"
+    # stainless_package_version: "0.80.0"
+    # stainless_runtime_version: "v24.13.0"
+    # stainless_os: "Linux"           # Linux / Darwin
+    # stainless_arch: "arm64"         # arm64 / x64
+
 # =============================================================================
 # Logging Configuration
 # 日志配置