diff --git a/internal/api/handlers/management/auth_files.go b/internal/api/handlers/management/auth_files.go
index 5d4026e8..68f71515 100644
--- a/internal/api/handlers/management/auth_files.go
+++ b/internal/api/handlers/management/auth_files.go
@@ -292,6 +292,7 @@ func (h *Handler) buildAuthFileEntry(auth *coreauth.Auth) gin.H {
 	if auth == nil {
 		return nil
 	}
+	auth.EnsureIndex()
 	runtimeOnly := isRuntimeOnlyAuth(auth)
 	if runtimeOnly && (auth.Disabled || auth.Status == coreauth.StatusDisabled) {
 		return nil
@@ -306,6 +307,7 @@ func (h *Handler) buildAuthFileEntry(auth *coreauth.Auth) gin.H {
 	}
 	entry := gin.H{
 		"id":             auth.ID,
+		"auth_index":     auth.Index,
 		"name":           name,
 		"type":           strings.TrimSpace(auth.Provider),
 		"provider":       strings.TrimSpace(auth.Provider),
diff --git a/internal/runtime/executor/iflow_executor.go b/internal/runtime/executor/iflow_executor.go
index 0ed6c0db..3589e922 100644
--- a/internal/runtime/executor/iflow_executor.go
+++ b/internal/runtime/executor/iflow_executor.go
@@ -112,6 +112,8 @@ func (e *IFlowExecutor) Execute(ctx context.Context, auth *cliproxyauth.Auth, re
 	}
 	appendAPIResponseChunk(ctx, e.cfg, data)
 	reporter.publish(ctx, parseOpenAIUsage(data))
+	// Ensure usage is recorded even if upstream omits usage metadata.
+	reporter.ensurePublished(ctx)
 
 	var param any
 	out := sdktranslator.TranslateNonStream(ctx, to, from, req.Model, bytes.Clone(opts.OriginalRequest), body, data, &param)
@@ -217,6 +219,8 @@ func (e *IFlowExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth.Au
 			reporter.publishFailure(ctx)
 			out <- cliproxyexecutor.StreamChunk{Err: errScan}
 		}
+		// Guarantee a usage record exists even if the stream never emitted usage data.
+		reporter.ensurePublished(ctx)
 	}()
 
 	return stream, nil
diff --git a/internal/runtime/executor/usage_helpers.go b/internal/runtime/executor/usage_helpers.go
index a3cd0922..be38355d 100644
--- a/internal/runtime/executor/usage_helpers.go
+++ b/internal/runtime/executor/usage_helpers.go
@@ -18,6 +18,7 @@ type usageReporter struct {
 	provider    string
 	model       string
 	authID      string
+	authIndex   uint64
 	apiKey      string
 	source      string
 	requestedAt time.Time
@@ -35,6 +36,7 @@ func newUsageReporter(ctx context.Context, provider, model string, auth *cliprox
 	}
 	if auth != nil {
 		reporter.authID = auth.ID
+		reporter.authIndex = auth.Index
 	}
 	return reporter
 }
@@ -76,6 +78,7 @@ func (r *usageReporter) publishWithOutcome(ctx context.Context, detail usage.Det
 			Source:      r.source,
 			APIKey:      r.apiKey,
 			AuthID:      r.authID,
+			AuthIndex:   r.authIndex,
 			RequestedAt: r.requestedAt,
 			Failed:      failed,
 			Detail:      detail,
@@ -98,6 +101,7 @@ func (r *usageReporter) ensurePublished(ctx context.Context) {
 			Source:      r.source,
 			APIKey:      r.apiKey,
 			AuthID:      r.authID,
+			AuthIndex:   r.authIndex,
 			RequestedAt: r.requestedAt,
 			Failed:      false,
 			Detail:      usage.Detail{},
diff --git a/internal/usage/logger_plugin.go b/internal/usage/logger_plugin.go
index 64c61d87..141ad997 100644
--- a/internal/usage/logger_plugin.go
+++ b/internal/usage/logger_plugin.go
@@ -90,6 +90,7 @@ type modelStats struct {
 type RequestDetail struct {
 	Timestamp time.Time  `json:"timestamp"`
 	Source    string     `json:"source"`
+	AuthIndex uint64     `json:"auth_index"`
 	Tokens    TokenStats `json:"tokens"`
 	Failed    bool       `json:"failed"`
 }
@@ -197,6 +198,7 @@ func (s *RequestStatistics) Record(ctx context.Context, record coreusage.Record)
 	s.updateAPIStats(stats, modelName, RequestDetail{
 		Timestamp: timestamp,
 		Source:    record.Source,
+		AuthIndex: record.AuthIndex,
 		Tokens:    detail,
 		Failed:    failed,
 	})
diff --git a/sdk/cliproxy/auth/manager.go b/sdk/cliproxy/auth/manager.go
index fe41cfe3..f195c0e9 100644
--- a/sdk/cliproxy/auth/manager.go
+++ b/sdk/cliproxy/auth/manager.go
@@ -169,6 +169,7 @@ 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()
 	}
@@ -185,6 +186,7 @@ func (m *Manager) Update(ctx context.Context, auth *Auth) (*Auth, error) {
 	if auth == nil || auth.ID == "" {
 		return nil, nil
 	}
+	auth.EnsureIndex()
 	m.mu.Lock()
 	m.auths[auth.ID] = auth.Clone()
 	m.mu.Unlock()
@@ -209,6 +211,7 @@ func (m *Manager) Load(ctx context.Context) error {
 		if auth == nil || auth.ID == "" {
 			continue
 		}
+		auth.EnsureIndex()
 		m.auths[auth.ID] = auth.Clone()
 	}
 	return nil
diff --git a/sdk/cliproxy/auth/types.go b/sdk/cliproxy/auth/types.go
index 8984554d..25e88b96 100644
--- a/sdk/cliproxy/auth/types.go
+++ b/sdk/cliproxy/auth/types.go
@@ -5,6 +5,7 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	baseauth "github.com/router-for-me/CLIProxyAPI/v6/internal/auth"
@@ -14,6 +15,8 @@ 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:"-"`
 	// Provider is the upstream provider key (e.g. "gemini", "claude").
 	Provider string `json:"provider"`
 	// FileName stores the relative or absolute path of the backing auth file.
@@ -55,6 +58,8 @@ type Auth struct {
 
 	// Runtime carries non-serialisable data used during execution (in-memory only).
 	Runtime any `json:"-"`
+
+	indexAssigned bool `json:"-"`
 }
 
 // QuotaState contains limiter tracking data for a credential.
@@ -87,6 +92,12 @@ 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 {
@@ -115,6 +126,20 @@ 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 {
+	if a == nil {
+		return 0
+	}
+	if a.indexAssigned {
+		return a.Index
+	}
+	idx := nextAuthIndex()
+	a.Index = idx
+	a.indexAssigned = true
+	return idx
+}
+
 // Clone duplicates a model state including nested error details.
 func (m *ModelState) Clone() *ModelState {
 	if m == nil {
diff --git a/sdk/cliproxy/usage/manager.go b/sdk/cliproxy/usage/manager.go
index 9ef73356..9e81cae5 100644
--- a/sdk/cliproxy/usage/manager.go
+++ b/sdk/cliproxy/usage/manager.go
@@ -14,6 +14,7 @@ type Record struct {
 	Model       string
 	APIKey      string
 	AuthID      string
+	AuthIndex   uint64
 	Source      string
 	RequestedAt time.Time
 	Failed      bool