diff --git a/internal/api/handlers/management/usage.go b/internal/api/handlers/management/usage.go
index e9c7dd209..5f7940896 100644
--- a/internal/api/handlers/management/usage.go
+++ b/internal/api/handlers/management/usage.go
@@ -1,12 +1,25 @@
 package management
 
 import (
+	"encoding/json"
 	"net/http"
+	"time"
 
 	"github.com/gin-gonic/gin"
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/usage"
 )
 
+type usageExportPayload struct {
+	Version    int                      `json:"version"`
+	ExportedAt time.Time                `json:"exported_at"`
+	Usage      usage.StatisticsSnapshot `json:"usage"`
+}
+
+type usageImportPayload struct {
+	Version int                      `json:"version"`
+	Usage   usage.StatisticsSnapshot `json:"usage"`
+}
+
 // GetUsageStatistics returns the in-memory request statistics snapshot.
 func (h *Handler) GetUsageStatistics(c *gin.Context) {
 	var snapshot usage.StatisticsSnapshot
@@ -18,3 +31,49 @@ func (h *Handler) GetUsageStatistics(c *gin.Context) {
 		"failed_requests": snapshot.FailureCount,
 	})
 }
+
+// ExportUsageStatistics returns a complete usage snapshot for backup/migration.
+func (h *Handler) ExportUsageStatistics(c *gin.Context) {
+	var snapshot usage.StatisticsSnapshot
+	if h != nil && h.usageStats != nil {
+		snapshot = h.usageStats.Snapshot()
+	}
+	c.JSON(http.StatusOK, usageExportPayload{
+		Version:    1,
+		ExportedAt: time.Now().UTC(),
+		Usage:      snapshot,
+	})
+}
+
+// ImportUsageStatistics merges a previously exported usage snapshot into memory.
+func (h *Handler) ImportUsageStatistics(c *gin.Context) {
+	if h == nil || h.usageStats == nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "usage statistics unavailable"})
+		return
+	}
+
+	data, err := c.GetRawData()
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "failed to read request body"})
+		return
+	}
+
+	var payload usageImportPayload
+	if err := json.Unmarshal(data, &payload); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid json"})
+		return
+	}
+	if payload.Version != 0 && payload.Version != 1 {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "unsupported version"})
+		return
+	}
+
+	result := h.usageStats.MergeSnapshot(payload.Usage)
+	snapshot := h.usageStats.Snapshot()
+	c.JSON(http.StatusOK, gin.H{
+		"added":           result.Added,
+		"skipped":         result.Skipped,
+		"total_requests":  snapshot.TotalRequests,
+		"failed_requests": snapshot.FailureCount,
+	})
+}
diff --git a/internal/api/server.go b/internal/api/server.go
index ef4559617..06a6c8cd1 100644
--- a/internal/api/server.go
+++ b/internal/api/server.go
@@ -496,6 +496,8 @@ func (s *Server) registerManagementRoutes() {
 	mgmt.Use(s.managementAvailabilityMiddleware(), s.mgmt.Middleware())
 	{
 		mgmt.GET("/usage", s.mgmt.GetUsageStatistics)
+		mgmt.GET("/usage/export", s.mgmt.ExportUsageStatistics)
+		mgmt.POST("/usage/import", s.mgmt.ImportUsageStatistics)
 		mgmt.GET("/config", s.mgmt.GetConfig)
 		mgmt.GET("/config.yaml", s.mgmt.GetConfigYAML)
 		mgmt.PUT("/config.yaml", s.mgmt.PutConfigYAML)
diff --git a/internal/runtime/executor/usage_helpers.go b/internal/runtime/executor/usage_helpers.go
index 78581b827..3bb5cb964 100644
--- a/internal/runtime/executor/usage_helpers.go
+++ b/internal/runtime/executor/usage_helpers.go
@@ -19,7 +19,7 @@ type usageReporter struct {
 	provider    string
 	model       string
 	authID      string
-	authIndex   uint64
+	authIndex   string
 	apiKey      string
 	source      string
 	requestedAt time.Time
diff --git a/internal/usage/logger_plugin.go b/internal/usage/logger_plugin.go
index 141ad9972..e4371e8d3 100644
--- a/internal/usage/logger_plugin.go
+++ b/internal/usage/logger_plugin.go
@@ -6,6 +6,7 @@ package usage
 import (
 	"context"
 	"fmt"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -90,7 +91,7 @@ type modelStats struct {
 type RequestDetail struct {
 	Timestamp time.Time  `json:"timestamp"`
 	Source    string     `json:"source"`
-	AuthIndex uint64     `json:"auth_index"`
+	AuthIndex string     `json:"auth_index"`
 	Tokens    TokenStats `json:"tokens"`
 	Failed    bool       `json:"failed"`
 }
@@ -281,6 +282,118 @@ func (s *RequestStatistics) Snapshot() StatisticsSnapshot {
 	return result
 }
 
+type MergeResult struct {
+	Added   int64 `json:"added"`
+	Skipped int64 `json:"skipped"`
+}
+
+// MergeSnapshot merges an exported statistics snapshot into the current store.
+// Existing data is preserved and duplicate request details are skipped.
+func (s *RequestStatistics) MergeSnapshot(snapshot StatisticsSnapshot) MergeResult {
+	result := MergeResult{}
+	if s == nil {
+		return result
+	}
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	seen := make(map[string]struct{})
+	for apiName, stats := range s.apis {
+		if stats == nil {
+			continue
+		}
+		for modelName, modelStatsValue := range stats.Models {
+			if modelStatsValue == nil {
+				continue
+			}
+			for _, detail := range modelStatsValue.Details {
+				seen[dedupKey(apiName, modelName, detail)] = struct{}{}
+			}
+		}
+	}
+
+	for apiName, apiSnapshot := range snapshot.APIs {
+		apiName = strings.TrimSpace(apiName)
+		if apiName == "" {
+			continue
+		}
+		stats, ok := s.apis[apiName]
+		if !ok || stats == nil {
+			stats = &apiStats{Models: make(map[string]*modelStats)}
+			s.apis[apiName] = stats
+		} else if stats.Models == nil {
+			stats.Models = make(map[string]*modelStats)
+		}
+		for modelName, modelSnapshot := range apiSnapshot.Models {
+			modelName = strings.TrimSpace(modelName)
+			if modelName == "" {
+				modelName = "unknown"
+			}
+			for _, detail := range modelSnapshot.Details {
+				detail.Tokens = normaliseTokenStats(detail.Tokens)
+				if detail.Timestamp.IsZero() {
+					detail.Timestamp = time.Now()
+				}
+				key := dedupKey(apiName, modelName, detail)
+				if _, exists := seen[key]; exists {
+					result.Skipped++
+					continue
+				}
+				seen[key] = struct{}{}
+				s.recordImported(apiName, modelName, stats, detail)
+				result.Added++
+			}
+		}
+	}
+
+	return result
+}
+
+func (s *RequestStatistics) recordImported(apiName, modelName string, stats *apiStats, detail RequestDetail) {
+	totalTokens := detail.Tokens.TotalTokens
+	if totalTokens < 0 {
+		totalTokens = 0
+	}
+
+	s.totalRequests++
+	if detail.Failed {
+		s.failureCount++
+	} else {
+		s.successCount++
+	}
+	s.totalTokens += totalTokens
+
+	s.updateAPIStats(stats, modelName, detail)
+
+	dayKey := detail.Timestamp.Format("2006-01-02")
+	hourKey := detail.Timestamp.Hour()
+
+	s.requestsByDay[dayKey]++
+	s.requestsByHour[hourKey]++
+	s.tokensByDay[dayKey] += totalTokens
+	s.tokensByHour[hourKey] += totalTokens
+}
+
+func dedupKey(apiName, modelName string, detail RequestDetail) string {
+	timestamp := detail.Timestamp.UTC().Format(time.RFC3339Nano)
+	tokens := normaliseTokenStats(detail.Tokens)
+	return fmt.Sprintf(
+		"%s|%s|%s|%s|%s|%t|%d|%d|%d|%d|%d",
+		apiName,
+		modelName,
+		timestamp,
+		detail.Source,
+		detail.AuthIndex,
+		detail.Failed,
+		tokens.InputTokens,
+		tokens.OutputTokens,
+		tokens.ReasoningTokens,
+		tokens.CachedTokens,
+		tokens.TotalTokens,
+	)
+}
+
 func resolveAPIIdentifier(ctx context.Context, record coreusage.Record) string {
 	if ctx != nil {
 		if ginCtx, ok := ctx.Value("gin").(*gin.Context); ok && ginCtx != nil {
@@ -340,6 +453,16 @@ func normaliseDetail(detail coreusage.Detail) TokenStats {
 	return tokens
 }
 
+func normaliseTokenStats(tokens TokenStats) TokenStats {
+	if tokens.TotalTokens == 0 {
+		tokens.TotalTokens = tokens.InputTokens + tokens.OutputTokens + tokens.ReasoningTokens
+	}
+	if tokens.TotalTokens == 0 {
+		tokens.TotalTokens = tokens.InputTokens + tokens.OutputTokens + tokens.ReasoningTokens + tokens.CachedTokens
+	}
+	return tokens
+}
+
 func formatHour(hour int) string {
 	if hour < 0 {
 		hour = 0
diff --git a/sdk/cliproxy/auth/conductor.go b/sdk/cliproxy/auth/conductor.go
index e2d4bbf10..b517e74ac 100644
--- a/sdk/cliproxy/auth/conductor.go
+++ b/sdk/cliproxy/auth/conductor.go
@@ -203,10 +203,10 @@ func (m *Manager) Register(ctx context.Context, auth *Auth) (*Auth, error) {
 	if auth == nil {
 		return nil, nil
 	}
-	auth.EnsureIndex()
 	if auth.ID == "" {
 		auth.ID = uuid.NewString()
 	}
+	auth.EnsureIndex()
 	m.mu.Lock()
 	m.auths[auth.ID] = auth.Clone()
 	m.mu.Unlock()
@@ -221,7 +221,7 @@ func (m *Manager) Update(ctx context.Context, auth *Auth) (*Auth, error) {
 		return nil, nil
 	}
 	m.mu.Lock()
-	if existing, ok := m.auths[auth.ID]; ok && existing != nil && !auth.indexAssigned && auth.Index == 0 {
+	if existing, ok := m.auths[auth.ID]; ok && existing != nil && !auth.indexAssigned && auth.Index == "" {
 		auth.Index = existing.Index
 		auth.indexAssigned = existing.indexAssigned
 	}
diff --git a/sdk/cliproxy/auth/types.go b/sdk/cliproxy/auth/types.go
index 5a2d216d5..4c69ae905 100644
--- a/sdk/cliproxy/auth/types.go
+++ b/sdk/cliproxy/auth/types.go
@@ -1,11 +1,12 @@
 package auth
 
 import (
+	"crypto/sha256"
+	"encoding/hex"
 	"encoding/json"
 	"strconv"
 	"strings"
 	"sync"
-	"sync/atomic"
 	"time"
 
 	baseauth "github.com/router-for-me/CLIProxyAPI/v6/internal/auth"
@@ -15,8 +16,8 @@ import (
 type Auth struct {
 	// ID uniquely identifies the auth record across restarts.
 	ID string `json:"id"`
-	// Index is a monotonically increasing runtime identifier used for diagnostics.
-	Index uint64 `json:"-"`
+	// Index is a stable runtime identifier derived from auth metadata (not persisted).
+	Index string `json:"-"`
 	// Provider is the upstream provider key (e.g. "gemini", "claude").
 	Provider string `json:"provider"`
 	// Prefix optionally namespaces models for routing (e.g., "teamA/gemini-3-pro-preview").
@@ -94,12 +95,6 @@ type ModelState struct {
 	UpdatedAt time.Time `json:"updated_at"`
 }
 
-var authIndexCounter atomic.Uint64
-
-func nextAuthIndex() uint64 {
-	return authIndexCounter.Add(1) - 1
-}
-
 // Clone shallow copies the Auth structure, duplicating maps to avoid accidental mutation.
 func (a *Auth) Clone() *Auth {
 	if a == nil {
@@ -128,15 +123,41 @@ func (a *Auth) Clone() *Auth {
 	return &copyAuth
 }
 
-// EnsureIndex returns the global index, assigning one if it was not set yet.
-func (a *Auth) EnsureIndex() uint64 {
+func stableAuthIndex(seed string) string {
+	seed = strings.TrimSpace(seed)
+	if seed == "" {
+		return ""
+	}
+	sum := sha256.Sum256([]byte(seed))
+	return hex.EncodeToString(sum[:8])
+}
+
+// EnsureIndex returns a stable index derived from the auth file name or API key.
+func (a *Auth) EnsureIndex() string {
 	if a == nil {
-		return 0
+		return ""
 	}
-	if a.indexAssigned {
+	if a.indexAssigned && a.Index != "" {
 		return a.Index
 	}
-	idx := nextAuthIndex()
+
+	seed := strings.TrimSpace(a.FileName)
+	if seed != "" {
+		seed = "file:" + seed
+	} else if a.Attributes != nil {
+		if apiKey := strings.TrimSpace(a.Attributes["api_key"]); apiKey != "" {
+			seed = "api_key:" + apiKey
+		}
+	}
+	if seed == "" {
+		if id := strings.TrimSpace(a.ID); id != "" {
+			seed = "id:" + id
+		} else {
+			return ""
+		}
+	}
+
+	idx := stableAuthIndex(seed)
 	a.Index = idx
 	a.indexAssigned = true
 	return idx
diff --git a/sdk/cliproxy/usage/manager.go b/sdk/cliproxy/usage/manager.go
index 9e81cae59..58b036076 100644
--- a/sdk/cliproxy/usage/manager.go
+++ b/sdk/cliproxy/usage/manager.go
@@ -14,7 +14,7 @@ type Record struct {
 	Model       string
 	APIKey      string
 	AuthID      string
-	AuthIndex   uint64
+	AuthIndex   string
 	Source      string
 	RequestedAt time.Time
 	Failed      bool