diff --git a/backend/internal/handler/admin/account_handler.go b/backend/internal/handler/admin/account_handler.go
index 78b71431..af1e7d91 100644
--- a/backend/internal/handler/admin/account_handler.go
+++ b/backend/internal/handler/admin/account_handler.go
@@ -3,7 +3,7 @@ package admin
 import (
 	"strconv"
 	"strings"
-	"time"
+	"sync"
 
 	"github.com/Wei-Shaw/sub2api/internal/handler/dto"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/claude"
@@ -14,6 +14,7 @@ import (
 	"github.com/Wei-Shaw/sub2api/internal/service"
 
 	"github.com/gin-gonic/gin"
+	"golang.org/x/sync/errgroup"
 )
 
 // OAuthHandler handles OAuth-related operations for accounts
@@ -1000,47 +1001,33 @@ func (h *AccountHandler) RefreshTier(c *gin.Context) {
 		return
 	}
 
-	account, err := h.adminService.GetAccount(c.Request.Context(), accountID)
+	ctx := c.Request.Context()
+	account, err := h.adminService.GetAccount(ctx, accountID)
 	if err != nil {
 		response.NotFound(c, "Account not found")
 		return
 	}
 
-	if account.Credentials == nil || account.Credentials["oauth_type"] != "google_one" {
-		response.BadRequest(c, "Account is not a google_one OAuth account")
+	if account.Platform != service.PlatformGemini || account.Type != service.AccountTypeOAuth {
+		response.BadRequest(c, "Only Gemini OAuth accounts support tier refresh")
 		return
 	}
 
-	accessToken, ok := account.Credentials["access_token"].(string)
-	if !ok || accessToken == "" {
-		response.BadRequest(c, "Missing access_token in credentials")
+	oauthType, _ := account.Credentials["oauth_type"].(string)
+	if oauthType != "google_one" {
+		response.BadRequest(c, "Only google_one OAuth accounts support tier refresh")
 		return
 	}
 
-	var proxyURL string
-	if account.ProxyID != nil && account.Proxy != nil {
-		proxyURL = account.Proxy.URL()
-	}
-
-	tierID, storageInfo, err := h.geminiOAuthService.FetchGoogleOneTier(c.Request.Context(), accessToken, proxyURL)
+	tierID, extra, creds, err := h.geminiOAuthService.RefreshAccountGoogleOneTier(ctx, account)
 	if err != nil {
 		response.ErrorFrom(c, err)
 		return
 	}
 
-	if account.Extra == nil {
-		account.Extra = make(map[string]any)
-	}
-	if storageInfo != nil {
-		account.Extra["drive_storage_limit"] = storageInfo.Limit
-		account.Extra["drive_storage_usage"] = storageInfo.Usage
-		account.Extra["drive_tier_updated_at"] = timezone.Now().Format(time.RFC3339)
-	}
-	account.Credentials["tier_id"] = tierID
-
-	_, updateErr := h.adminService.UpdateAccount(c.Request.Context(), accountID, &service.UpdateAccountInput{
-		Credentials: account.Credentials,
-		Extra:       account.Extra,
+	_, updateErr := h.adminService.UpdateAccount(ctx, accountID, &service.UpdateAccountInput{
+		Credentials: creds,
+		Extra:       extra,
 	})
 	if updateErr != nil {
 		response.ErrorFrom(c, updateErr)
@@ -1049,9 +1036,10 @@ func (h *AccountHandler) RefreshTier(c *gin.Context) {
 
 	response.Success(c, gin.H{
 		"tier_id":             tierID,
-		"drive_storage_limit": account.Extra["drive_storage_limit"],
-		"drive_storage_usage": account.Extra["drive_storage_usage"],
-		"updated_at":          account.Extra["drive_tier_updated_at"],
+		"storage_info":        extra,
+		"drive_storage_limit": extra["drive_storage_limit"],
+		"drive_storage_usage": extra["drive_storage_usage"],
+		"updated_at":          extra["drive_tier_updated_at"],
 	})
 }
 
@@ -1069,7 +1057,7 @@ func (h *AccountHandler) BatchRefreshTier(c *gin.Context) {
 	}
 
 	ctx := c.Request.Context()
-	var accounts []service.Account
+	accounts := make([]*service.Account, 0)
 
 	if len(req.AccountIDs) == 0 {
 		allAccounts, _, err := h.adminService.ListAccounts(ctx, 1, 10000, "gemini", "oauth", "", "")
@@ -1077,84 +1065,87 @@ func (h *AccountHandler) BatchRefreshTier(c *gin.Context) {
 			response.ErrorFrom(c, err)
 			return
 		}
-		for _, acc := range allAccounts {
-			if acc.Credentials != nil && acc.Credentials["oauth_type"] == "google_one" {
+		for i := range allAccounts {
+			acc := &allAccounts[i]
+			oauthType, _ := acc.Credentials["oauth_type"].(string)
+			if oauthType == "google_one" {
 				accounts = append(accounts, acc)
 			}
 		}
 	} else {
-		for _, id := range req.AccountIDs {
-			acc, err := h.adminService.GetAccount(ctx, id)
-			if err != nil {
+		fetched, err := h.adminService.GetAccountsByIDs(ctx, req.AccountIDs)
+		if err != nil {
+			response.ErrorFrom(c, err)
+			return
+		}
+
+		for _, acc := range fetched {
+			if acc == nil {
 				continue
 			}
-			if acc.Credentials != nil && acc.Credentials["oauth_type"] == "google_one" {
-				accounts = append(accounts, *acc)
+			if acc.Platform != service.PlatformGemini || acc.Type != service.AccountTypeOAuth {
+				continue
 			}
+			oauthType, _ := acc.Credentials["oauth_type"].(string)
+			if oauthType != "google_one" {
+				continue
+			}
+			accounts = append(accounts, acc)
 		}
 	}
 
-	total := len(accounts)
-	success := 0
-	failed := 0
-	errors := []gin.H{}
+	const maxConcurrency = 10
+	g, gctx := errgroup.WithContext(ctx)
+	g.SetLimit(maxConcurrency)
+
+	var mu sync.Mutex
+	results := gin.H{
+		"total":   len(accounts),
+		"success": 0,
+		"failed":  0,
+		"errors":  []gin.H{},
+	}
 
 	for _, account := range accounts {
-		accessToken, ok := account.Credentials["access_token"].(string)
-		if !ok || accessToken == "" {
-			failed++
-			errors = append(errors, gin.H{
-				"account_id": account.ID,
-				"error":      "missing access_token",
+		acc := account // 闭包捕获
+		g.Go(func() error {
+			_, extra, creds, err := h.geminiOAuthService.RefreshAccountGoogleOneTier(gctx, acc)
+			if err != nil {
+				mu.Lock()
+				results["failed"] = results["failed"].(int) + 1
+				results["errors"] = append(results["errors"].([]gin.H), gin.H{
+					"account_id": acc.ID,
+					"error":      err.Error(),
+				})
+				mu.Unlock()
+				return nil
+			}
+
+			_, updateErr := h.adminService.UpdateAccount(gctx, acc.ID, &service.UpdateAccountInput{
+				Credentials: creds,
+				Extra:       extra,
 			})
-			continue
-		}
 
-		var proxyURL string
-		if account.ProxyID != nil && account.Proxy != nil {
-			proxyURL = account.Proxy.URL()
-		}
+			mu.Lock()
+			if updateErr != nil {
+				results["failed"] = results["failed"].(int) + 1
+				results["errors"] = append(results["errors"].([]gin.H), gin.H{
+					"account_id": acc.ID,
+					"error":      updateErr.Error(),
+				})
+			} else {
+				results["success"] = results["success"].(int) + 1
+			}
+			mu.Unlock()
 
-		tierID, storageInfo, err := h.geminiOAuthService.FetchGoogleOneTier(ctx, accessToken, proxyURL)
-		if err != nil {
-			failed++
-			errors = append(errors, gin.H{
-				"account_id": account.ID,
-				"error":      err.Error(),
-			})
-			continue
-		}
-
-		if account.Extra == nil {
-			account.Extra = make(map[string]any)
-		}
-		if storageInfo != nil {
-			account.Extra["drive_storage_limit"] = storageInfo.Limit
-			account.Extra["drive_storage_usage"] = storageInfo.Usage
-			account.Extra["drive_tier_updated_at"] = timezone.Now().Format(time.RFC3339)
-		}
-		account.Credentials["tier_id"] = tierID
-
-		_, updateErr := h.adminService.UpdateAccount(ctx, account.ID, &service.UpdateAccountInput{
-			Credentials: account.Credentials,
-			Extra:       account.Extra,
+			return nil
 		})
-		if updateErr != nil {
-			failed++
-			errors = append(errors, gin.H{
-				"account_id": account.ID,
-				"error":      updateErr.Error(),
-			})
-			continue
-		}
-
-		success++
 	}
 
-	response.Success(c, gin.H{
-		"total":   total,
-		"success": success,
-		"failed":  failed,
-		"errors":  errors,
-	})
+	if err := g.Wait(); err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+
+	response.Success(c, results)
 }
diff --git a/backend/internal/pkg/geminicli/drive_client.go b/backend/internal/pkg/geminicli/drive_client.go
index 79d6835f..77e2c476 100644
--- a/backend/internal/pkg/geminicli/drive_client.go
+++ b/backend/internal/pkg/geminicli/drive_client.go
@@ -5,7 +5,9 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"math/rand"
 	"net/http"
+	"strconv"
 	"time"
 
 	"github.com/Wei-Shaw/sub2api/internal/pkg/httpclient"
@@ -49,13 +51,38 @@ func (c *driveClient) GetStorageQuota(ctx context.Context, accessToken, proxyURL
 		return nil, fmt.Errorf("failed to create HTTP client: %w", err)
 	}
 
-	// Retry logic with exponential backoff for rate limits
+	sleepWithContext := func(d time.Duration) error {
+		timer := time.NewTimer(d)
+		defer timer.Stop()
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-timer.C:
+			return nil
+		}
+	}
+
+	// Retry logic with exponential backoff (+ jitter) for rate limits and transient failures
 	var resp *http.Response
 	maxRetries := 3
+	rng := rand.New(rand.NewSource(time.Now().UnixNano()))
 	for attempt := 0; attempt < maxRetries; attempt++ {
+		if ctx.Err() != nil {
+			return nil, fmt.Errorf("request cancelled: %w", ctx.Err())
+		}
+
 		resp, err = client.Do(req)
 		if err != nil {
-			return nil, fmt.Errorf("failed to execute request: %w", err)
+			// Network error retry
+			if attempt < maxRetries-1 {
+				backoff := time.Duration(1<<uint(attempt)) * time.Second
+				jitter := time.Duration(rng.Intn(1000)) * time.Millisecond
+				if err := sleepWithContext(backoff + jitter); err != nil {
+					return nil, fmt.Errorf("request cancelled: %w", err)
+				}
+				continue
+			}
+			return nil, fmt.Errorf("network error after %d attempts: %w", maxRetries, err)
 		}
 
 		// Success
@@ -63,18 +90,34 @@ func (c *driveClient) GetStorageQuota(ctx context.Context, accessToken, proxyURL
 			break
 		}
 
-		// Rate limit - retry with exponential backoff
-		if resp.StatusCode == http.StatusTooManyRequests && attempt < maxRetries-1 {
+		// Retry 429, 500, 502, 503 with exponential backoff + jitter
+		if (resp.StatusCode == http.StatusTooManyRequests ||
+			resp.StatusCode == http.StatusInternalServerError ||
+			resp.StatusCode == http.StatusBadGateway ||
+			resp.StatusCode == http.StatusServiceUnavailable) && attempt < maxRetries-1 {
 			_ = resp.Body.Close()
-			backoff := time.Duration(1<<uint(attempt)) * time.Second // 1s, 2s, 4s
-			time.Sleep(backoff)
+			backoff := time.Duration(1<<uint(attempt)) * time.Second
+			jitter := time.Duration(rng.Intn(1000)) * time.Millisecond
+			if err := sleepWithContext(backoff + jitter); err != nil {
+				return nil, fmt.Errorf("request cancelled: %w", err)
+			}
 			continue
 		}
 
-		// Other errors - return immediately
+		break
+	}
+
+	if resp == nil {
+		return nil, fmt.Errorf("request failed: no response received")
+	}
+
+	if resp.StatusCode != http.StatusOK {
 		body, _ := io.ReadAll(resp.Body)
 		_ = resp.Body.Close()
-		return nil, fmt.Errorf("drive API error (status %d): %s", resp.StatusCode, string(body))
+		// 记录完整错误
+		fmt.Printf("[DriveClient] API error (status %d): %s\n", resp.StatusCode, string(body))
+		// 只返回通用错误
+		return nil, fmt.Errorf("drive API error: status %d", resp.StatusCode)
 	}
 
 	defer func() { _ = resp.Body.Close() }()
@@ -94,10 +137,14 @@ func (c *driveClient) GetStorageQuota(ctx context.Context, accessToken, proxyURL
 	// Parse limit and usage (handle both string and number formats)
 	var limit, usage int64
 	if result.StorageQuota.Limit != "" {
-		_, _ = fmt.Sscanf(result.StorageQuota.Limit, "%d", &limit)
+		if val, err := strconv.ParseInt(result.StorageQuota.Limit, 10, 64); err == nil {
+			limit = val
+		}
 	}
 	if result.StorageQuota.Usage != "" {
-		_, _ = fmt.Sscanf(result.StorageQuota.Usage, "%d", &usage)
+		if val, err := strconv.ParseInt(result.StorageQuota.Usage, 10, 64); err == nil {
+			usage = val
+		}
 	}
 
 	return &DriveStorageInfo{
diff --git a/backend/internal/pkg/geminicli/drive_client_test.go b/backend/internal/pkg/geminicli/drive_client_test.go
new file mode 100644
index 00000000..d2c7f25b
--- /dev/null
+++ b/backend/internal/pkg/geminicli/drive_client_test.go
@@ -0,0 +1,19 @@
+package geminicli
+
+import "testing"
+
+func TestDriveStorageInfo(t *testing.T) {
+	// 测试 DriveStorageInfo 结构体
+	info := &DriveStorageInfo{
+		Limit: 100 * 1024 * 1024 * 1024, // 100GB
+		Usage: 50 * 1024 * 1024 * 1024,  // 50GB
+	}
+
+	if info.Limit != 100*1024*1024*1024 {
+		t.Errorf("Expected limit 100GB, got %d", info.Limit)
+	}
+	if info.Usage != 50*1024*1024*1024 {
+		t.Errorf("Expected usage 50GB, got %d", info.Usage)
+	}
+}
+
diff --git a/backend/internal/repository/account_repo.go b/backend/internal/repository/account_repo.go
index 631f4ee4..63bd6abb 100644
--- a/backend/internal/repository/account_repo.go
+++ b/backend/internal/repository/account_repo.go
@@ -124,6 +124,90 @@ func (r *accountRepository) GetByID(ctx context.Context, id int64) (*service.Acc
 	return &accounts[0], nil
 }
 
+func (r *accountRepository) GetByIDs(ctx context.Context, ids []int64) ([]*service.Account, error) {
+	if len(ids) == 0 {
+		return []*service.Account{}, nil
+	}
+
+	// De-duplicate while preserving order of first occurrence.
+	uniqueIDs := make([]int64, 0, len(ids))
+	seen := make(map[int64]struct{}, len(ids))
+	for _, id := range ids {
+		if id <= 0 {
+			continue
+		}
+		if _, ok := seen[id]; ok {
+			continue
+		}
+		seen[id] = struct{}{}
+		uniqueIDs = append(uniqueIDs, id)
+	}
+	if len(uniqueIDs) == 0 {
+		return []*service.Account{}, nil
+	}
+
+	entAccounts, err := r.client.Account.
+		Query().
+		Where(dbaccount.IDIn(uniqueIDs...)).
+		WithProxy().
+		All(ctx)
+	if err != nil {
+		return nil, err
+	}
+	if len(entAccounts) == 0 {
+		return []*service.Account{}, nil
+	}
+
+	accountIDs := make([]int64, 0, len(entAccounts))
+	entByID := make(map[int64]*dbent.Account, len(entAccounts))
+	for _, acc := range entAccounts {
+		entByID[acc.ID] = acc
+		accountIDs = append(accountIDs, acc.ID)
+	}
+
+	groupsByAccount, groupIDsByAccount, accountGroupsByAccount, err := r.loadAccountGroups(ctx, accountIDs)
+	if err != nil {
+		return nil, err
+	}
+
+	outByID := make(map[int64]*service.Account, len(entAccounts))
+	for _, entAcc := range entAccounts {
+		out := accountEntityToService(entAcc)
+		if out == nil {
+			continue
+		}
+
+		// Prefer the preloaded proxy edge when available.
+		if entAcc.Edges.Proxy != nil {
+			out.Proxy = proxyEntityToService(entAcc.Edges.Proxy)
+		}
+
+		if groups, ok := groupsByAccount[entAcc.ID]; ok {
+			out.Groups = groups
+		}
+		if groupIDs, ok := groupIDsByAccount[entAcc.ID]; ok {
+			out.GroupIDs = groupIDs
+		}
+		if ags, ok := accountGroupsByAccount[entAcc.ID]; ok {
+			out.AccountGroups = ags
+		}
+		outByID[entAcc.ID] = out
+	}
+
+	// Preserve input order (first occurrence), and ignore missing IDs.
+	out := make([]*service.Account, 0, len(uniqueIDs))
+	for _, id := range uniqueIDs {
+		if _, ok := entByID[id]; !ok {
+			continue
+		}
+		if acc, ok := outByID[id]; ok && acc != nil {
+			out = append(out, acc)
+		}
+	}
+
+	return out, nil
+}
+
 // ExistsByID 检查指定 ID 的账号是否存在。
 // 相比 GetByID，此方法性能更优，因为：
 //   - 使用 Exist() 方法生成 SELECT EXISTS 查询，只返回布尔值
diff --git a/backend/internal/service/account_service.go b/backend/internal/service/account_service.go
index 3c5841bd..6a107155 100644
--- a/backend/internal/service/account_service.go
+++ b/backend/internal/service/account_service.go
@@ -17,6 +17,9 @@ var (
 type AccountRepository interface {
 	Create(ctx context.Context, account *Account) error
 	GetByID(ctx context.Context, id int64) (*Account, error)
+	// GetByIDs fetches accounts by IDs in a single query.
+	// It should return all accounts found (missing IDs are ignored).
+	GetByIDs(ctx context.Context, ids []int64) ([]*Account, error)
 	// ExistsByID 检查账号是否存在，仅返回布尔值，用于删除前的轻量级存在性检查
 	ExistsByID(ctx context.Context, id int64) (bool, error)
 	// GetByCRSAccountID finds an account previously synced from CRS.
diff --git a/backend/internal/service/admin_service.go b/backend/internal/service/admin_service.go
index feeb19a0..2f0f5f31 100644
--- a/backend/internal/service/admin_service.go
+++ b/backend/internal/service/admin_service.go
@@ -35,6 +35,7 @@ type AdminService interface {
 	// Account management
 	ListAccounts(ctx context.Context, page, pageSize int, platform, accountType, status, search string) ([]Account, int64, error)
 	GetAccount(ctx context.Context, id int64) (*Account, error)
+	GetAccountsByIDs(ctx context.Context, ids []int64) ([]*Account, error)
 	CreateAccount(ctx context.Context, input *CreateAccountInput) (*Account, error)
 	UpdateAccount(ctx context.Context, id int64, input *UpdateAccountInput) (*Account, error)
 	DeleteAccount(ctx context.Context, id int64) error
@@ -611,6 +612,19 @@ func (s *adminServiceImpl) GetAccount(ctx context.Context, id int64) (*Account,
 	return s.accountRepo.GetByID(ctx, id)
 }
 
+func (s *adminServiceImpl) GetAccountsByIDs(ctx context.Context, ids []int64) ([]*Account, error) {
+	if len(ids) == 0 {
+		return []*Account{}, nil
+	}
+
+	accounts, err := s.accountRepo.GetByIDs(ctx, ids)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get accounts by IDs: %w", err)
+	}
+
+	return accounts, nil
+}
+
 func (s *adminServiceImpl) CreateAccount(ctx context.Context, input *CreateAccountInput) (*Account, error) {
 	account := &Account{
 		Name:        input.Name,
diff --git a/backend/internal/service/gemini_oauth_service.go b/backend/internal/service/gemini_oauth_service.go
index a6b63924..e9ccae34 100644
--- a/backend/internal/service/gemini_oauth_service.go
+++ b/backend/internal/service/gemini_oauth_service.go
@@ -26,6 +26,17 @@ const (
 	TierGoogleOneUnlimited = "GOOGLE_ONE_UNLIMITED"
 )
 
+const (
+	GB = 1024 * 1024 * 1024
+	TB = 1024 * GB
+
+	StorageTierUnlimited = 100 * TB // 100TB
+	StorageTierAIPremium = 2 * TB   // 2TB
+	StorageTierStandard  = 200 * GB // 200GB
+	StorageTierBasic     = 100 * GB // 100GB
+	StorageTierFree      = 15 * GB  // 15GB
+)
+
 type GeminiOAuthService struct {
 	sessionStore *geminicli.SessionStore
 	proxyRepo    ProxyRepository
@@ -222,31 +233,21 @@ func inferGoogleOneTier(storageBytes int64) string {
 		return TierGoogleOneUnknown
 	}
 
-	// Unlimited storage (G Suite legacy)
-	if storageBytes > 100*1024*1024*1024*1024 { // > 100TB
+	if storageBytes > StorageTierUnlimited {
 		return TierGoogleOneUnlimited
 	}
-
-	// AI Premium (2TB+)
-	if storageBytes >= 2*1024*1024*1024*1024 { // >= 2TB
+	if storageBytes >= StorageTierAIPremium {
 		return TierAIPremium
 	}
-
-	// Google One Standard (200GB)
-	if storageBytes >= 200*1024*1024*1024 { // >= 200GB
+	if storageBytes >= StorageTierStandard {
 		return TierGoogleOneStandard
 	}
-
-	// Google One Basic (100GB)
-	if storageBytes >= 100*1024*1024*1024 { // >= 100GB
+	if storageBytes >= StorageTierBasic {
 		return TierGoogleOneBasic
 	}
-
-	// Free (15GB)
-	if storageBytes >= 15*1024*1024*1024 { // >= 15GB
+	if storageBytes >= StorageTierFree {
 		return TierFree
 	}
-
 	return TierGoogleOneUnknown
 }
 
@@ -270,6 +271,60 @@ func (s *GeminiOAuthService) FetchGoogleOneTier(ctx context.Context, accessToken
 	return tierID, storageInfo, nil
 }
 
+// RefreshAccountGoogleOneTier 刷新单个账号的 Google One Tier
+func (s *GeminiOAuthService) RefreshAccountGoogleOneTier(
+	ctx context.Context,
+	account *Account,
+) (tierID string, extra map[string]any, credentials map[string]any, err error) {
+	if account == nil {
+		return "", nil, nil, fmt.Errorf("account is nil")
+	}
+
+	// 验证账号类型
+	oauthType, ok := account.Credentials["oauth_type"].(string)
+	if !ok || oauthType != "google_one" {
+		return "", nil, nil, fmt.Errorf("not a google_one OAuth account")
+	}
+
+	// 获取 access_token
+	accessToken, ok := account.Credentials["access_token"].(string)
+	if !ok || accessToken == "" {
+		return "", nil, nil, fmt.Errorf("missing access_token")
+	}
+
+	// 获取 proxy URL
+	var proxyURL string
+	if account.ProxyID != nil && account.Proxy != nil {
+		proxyURL = account.Proxy.URL()
+	}
+
+	// 调用 Drive API
+	tierID, storageInfo, err := s.FetchGoogleOneTier(ctx, accessToken, proxyURL)
+	if err != nil {
+		return "", nil, nil, err
+	}
+
+	// 构建 extra 数据（保留原有 extra 字段）
+	extra = make(map[string]any)
+	for k, v := range account.Extra {
+		extra[k] = v
+	}
+	if storageInfo != nil {
+		extra["drive_storage_limit"] = storageInfo.Limit
+		extra["drive_storage_usage"] = storageInfo.Usage
+		extra["drive_tier_updated_at"] = time.Now().Format(time.RFC3339)
+	}
+
+	// 构建 credentials 数据
+	credentials = make(map[string]any)
+	for k, v := range account.Credentials {
+		credentials[k] = v
+	}
+	credentials["tier_id"] = tierID
+
+	return tierID, extra, credentials, nil
+}
+
 func (s *GeminiOAuthService) ExchangeCode(ctx context.Context, input *GeminiExchangeCodeInput) (*GeminiTokenInfo, error) {
 	session, ok := s.sessionStore.Get(input.SessionID)
 	if !ok {
diff --git a/backend/internal/service/gemini_oauth_service_test.go b/backend/internal/service/gemini_oauth_service_test.go
new file mode 100644
index 00000000..393812c2
--- /dev/null
+++ b/backend/internal/service/gemini_oauth_service_test.go
@@ -0,0 +1,52 @@
+package service
+
+import "testing"
+
+func TestInferGoogleOneTier(t *testing.T) {
+	tests := []struct {
+		name         string
+		storageBytes int64
+		expectedTier string
+	}{
+		{"Negative storage", -1, TierGoogleOneUnknown},
+		{"Zero storage", 0, TierGoogleOneUnknown},
+
+		// Free tier boundary (15GB)
+		{"Below free tier", 10 * GB, TierGoogleOneUnknown},
+		{"Just below free tier", StorageTierFree - 1, TierGoogleOneUnknown},
+		{"Free tier (15GB)", StorageTierFree, TierFree},
+
+		// Basic tier boundary (100GB)
+		{"Between free and basic", 50 * GB, TierFree},
+		{"Just below basic tier", StorageTierBasic - 1, TierFree},
+		{"Basic tier (100GB)", StorageTierBasic, TierGoogleOneBasic},
+
+		// Standard tier boundary (200GB)
+		{"Between basic and standard", 150 * GB, TierGoogleOneBasic},
+		{"Just below standard tier", StorageTierStandard - 1, TierGoogleOneBasic},
+		{"Standard tier (200GB)", StorageTierStandard, TierGoogleOneStandard},
+
+		// AI Premium tier boundary (2TB)
+		{"Between standard and premium", 1 * TB, TierGoogleOneStandard},
+		{"Just below AI Premium tier", StorageTierAIPremium - 1, TierGoogleOneStandard},
+		{"AI Premium tier (2TB)", StorageTierAIPremium, TierAIPremium},
+
+		// Unlimited tier boundary (> 100TB)
+		{"Between premium and unlimited", 50 * TB, TierAIPremium},
+		{"At unlimited threshold (100TB)", StorageTierUnlimited, TierAIPremium},
+		{"Unlimited tier (100TB+)", StorageTierUnlimited + 1, TierGoogleOneUnlimited},
+		{"Unlimited tier (101TB+)", 101 * TB, TierGoogleOneUnlimited},
+		{"Very large storage", 1000 * TB, TierGoogleOneUnlimited},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := inferGoogleOneTier(tt.storageBytes)
+			if result != tt.expectedTier {
+				t.Errorf("inferGoogleOneTier(%d) = %s, want %s",
+					tt.storageBytes, result, tt.expectedTier)
+			}
+		})
+	}
+}
+
diff --git a/backend/migrations/017_add_gemini_tier_id.sql b/backend/migrations/024_add_gemini_tier_id.sql
similarity index 94%
rename from backend/migrations/017_add_gemini_tier_id.sql
rename to backend/migrations/024_add_gemini_tier_id.sql
index 0388a412..d9ac7afe 100644
--- a/backend/migrations/017_add_gemini_tier_id.sql
+++ b/backend/migrations/024_add_gemini_tier_id.sql
@@ -26,5 +26,5 @@ UPDATE accounts
 SET credentials = credentials - 'tier_id'
 WHERE platform = 'gemini'
   AND type = 'oauth'
-  AND credentials->>'oauth_type' = 'code_assist';
+  AND credentials ? 'tier_id';
 -- +goose StatementEnd