diff --git a/.env.example b/.env.example
index dc2eafe7677..32179e02192 100644
--- a/.env.example
+++ b/.env.example
@@ -1156,6 +1156,11 @@ USE_ENTRA_ID_FOR_PEOPLE_SEARCH=false
 # When enabled, entra id groups owners will be considered as members of the group
 ENTRA_ID_INCLUDE_OWNERS_AS_MEMBERS=false
 
+# When enabled, login sync only updates membership of Entra ID groups already in the database
+# (e.g. created when a resource is shared with them) instead of creating every group the user is in
+# permissions.syncOnlyExistingEntraGroups in librechat.yaml takes precedence
+ENTRA_ID_SYNC_ONLY_EXISTING_GROUPS=false
+
 # Microsoft Graph API scopes needed for people/group search
 # Default scopes provide access to user profiles and group memberships
 OPENID_GRAPH_SCOPES=User.Read,People.Read,GroupMember.Read.All
diff --git a/api/server/controllers/auth/oauth.js b/api/server/controllers/auth/oauth.js
index e7df7661a28..ac9ecc28a21 100644
--- a/api/server/controllers/auth/oauth.js
+++ b/api/server/controllers/auth/oauth.js
@@ -5,9 +5,11 @@ const {
   getAdminPanelUrl,
   isAdminPanelRedirect,
   generateAdminExchangeCode,
+  getAppConfigOptionsFromUser,
 } = require('@librechat/api');
 const { syncUserEntraGroupMemberships } = require('~/server/services/PermissionService');
 const { setAuthTokens } = require('~/server/services/AuthService');
+const { getAppConfig } = require('~/server/services/Config');
 const { sendOpenIDAuthResponse } = require('~/server/services/OpenIDRefreshRecovery');
 const getLogStores = require('~/cache/getLogStores');
 const { checkBan } = require('~/server/middleware');
@@ -76,7 +78,13 @@ function createOAuthHandler(redirectUri = domains.client) {
         req.user.provider == 'openid' &&
         isEnabled(process.env.OPENID_REUSE_TOKENS) === true
       ) {
-        await syncUserEntraGroupMemberships(req.user, req.user.tokenset.access_token);
+        const appConfig = await getAppConfig(getAppConfigOptionsFromUser(req.user));
+        await syncUserEntraGroupMemberships(
+          req.user,
+          req.user.tokenset.access_token,
+          null,
+          appConfig,
+        );
         await sendOpenIDAuthResponse({
           tokenset: req.user.tokenset,
           user: req.user,
diff --git a/api/server/services/PermissionService.js b/api/server/services/PermissionService.js
index c525c0a0b86..25fdebbecce 100644
--- a/api/server/services/PermissionService.js
+++ b/api/server/services/PermissionService.js
@@ -1,5 +1,10 @@
 const mongoose = require('mongoose');
-const { AccessControlService, isEnabled, ensureDirectoryPrincipalUser } = require('@librechat/api');
+const {
+  isEnabled,
+  AccessControlService,
+  ensureDirectoryPrincipalUser,
+  syncsOnlyExistingEntraGroups,
+} = require('@librechat/api');
 const {
   tenantStorage,
   getTenantId,
@@ -483,7 +488,8 @@ const ensureGroupPrincipalExists = async function (principal, authContext = null
 
 /**
  * Sync user's Entra ID group memberships with auto-creation of missing groups
- * Optimized approach:
+ * Optimized approach (steps 4-6 are skipped when `permissions.syncOnlyExistingEntraGroups`
+ * or `ENTRA_ID_SYNC_ONLY_EXISTING_GROUPS` is enabled, so only existing groups are synced):
  * 1. Get all group IDs user should be member of from Entra
  * 2. Try to add user to existing groups (fast, no Graph API calls)
  * 3. Query DB to identify which groups don't exist (indexed query, fast)
@@ -498,12 +504,13 @@ const ensureGroupPrincipalExists = async function (principal, authContext = null
  * @param {string} user.provider - Authentication provider ('openid')
  * @param {string} accessToken - Access token for Graph API calls
  * @param {mongoose.ClientSession} [session] - Optional MongoDB session for transactions
+ * @param {AppConfig} [appConfig] - Resolved app config for the user
  * @returns {Promise<void>}
  */
-const syncUserEntraGroupMemberships = async (user, accessToken, session = null) => {
+const syncUserEntraGroupMemberships = async (user, accessToken, session = null, appConfig) => {
   const tenantId = user?.tenantId ? String(user.tenantId) : undefined;
   if (!tenantId || getTenantId() != null) {
-    return performEntraGroupMembershipSync(user, accessToken, session);
+    return performEntraGroupMembershipSync(user, accessToken, session, appConfig);
   }
   /**
    * The OAuth callback runs before `tenantContextMiddleware`, so establish the
@@ -511,11 +518,11 @@ const syncUserEntraGroupMemberships = async (user, accessToken, session = null)
    * cache invalidation are then scoped exactly like authenticated reads.
    */
   return tenantStorage.run({ tenantId, userId: user._id?.toString() }, async () =>
-    performEntraGroupMembershipSync(user, accessToken, session),
+    performEntraGroupMembershipSync(user, accessToken, session, appConfig),
   );
 };
 
-const performEntraGroupMembershipSync = async (user, accessToken, session = null) => {
+const performEntraGroupMembershipSync = async (user, accessToken, session = null, appConfig) => {
   try {
     if (!entraIdPrincipalFeatureEnabled(user) || !accessToken || !user.idOnTheSource) {
       return;
@@ -570,7 +577,16 @@ const performEntraGroupMembershipSync = async (user, accessToken, session = null
 
     const missingGroupIds = allGroupIds.filter((id) => !existingGroupIds.has(id));
 
-    if (missingGroupIds.length > 0) {
+    const syncOnlyExisting = syncsOnlyExistingEntraGroups(
+      appConfig?.config?.permissions,
+      process.env.ENTRA_ID_SYNC_ONLY_EXISTING_GROUPS,
+    );
+
+    if (missingGroupIds.length > 0 && syncOnlyExisting) {
+      logger.debug(
+        `[PermissionService.syncUserEntraGroupMemberships] Skipping ${missingGroupIds.length} groups not in database`,
+      );
+    } else if (missingGroupIds.length > 0) {
       logger.info(
         `[PermissionService.syncUserEntraGroupMemberships] Found ${missingGroupIds.length} groups that don't exist, fetching details...`,
       );
diff --git a/api/server/services/PermissionService.spec.js b/api/server/services/PermissionService.spec.js
index 604b03bfecf..34daa94a2f0 100644
--- a/api/server/services/PermissionService.spec.js
+++ b/api/server/services/PermissionService.spec.js
@@ -2536,4 +2536,76 @@ describe('syncUserEntraGroupMemberships - $pullAll on Group.memberIds', () => {
     // Reset mock
     getEntraGroupDetailsBatch.mockResolvedValue([]);
   });
+
+  describe('with ENTRA_ID_SYNC_ONLY_EXISTING_GROUPS enabled', () => {
+    const { getEntraGroupDetailsBatch } = require('~/server/services/GraphApiService');
+
+    beforeEach(() => {
+      process.env.ENTRA_ID_SYNC_ONLY_EXISTING_GROUPS = 'true';
+      getEntraGroupDetailsBatch.mockClear();
+    });
+
+    afterEach(() => {
+      delete process.env.ENTRA_ID_SYNC_ONLY_EXISTING_GROUPS;
+      getEntraGroupDetailsBatch.mockResolvedValue([]);
+    });
+
+    it('does not create groups missing from the database', async () => {
+      await Group.create({
+        name: 'Shared',
+        source: 'entra',
+        idOnTheSource: 'entra-shared',
+        memberIds: [],
+      });
+      getUserEntraGroups.mockResolvedValue(['entra-shared', 'entra-unused']);
+      getEntraGroupDetailsBatch.mockResolvedValue([{ id: 'entra-unused', name: 'Unused' }]);
+
+      await syncUserEntraGroupMemberships(user, 'fake-token');
+
+      expect(getEntraGroupDetailsBatch).not.toHaveBeenCalled();
+      expect(await Group.countDocuments({ idOnTheSource: 'entra-unused' })).toBe(0);
+      const shared = await Group.findOne({ idOnTheSource: 'entra-shared' }).lean();
+      expect(shared.memberIds).toContain(userEntraId);
+    });
+
+    it('still removes the user from existing groups they left', async () => {
+      await Group.create({
+        name: 'Left',
+        source: 'entra',
+        idOnTheSource: 'entra-left',
+        memberIds: [userEntraId],
+      });
+      getUserEntraGroups.mockResolvedValue(['entra-unused']);
+      getEntraGroupDetailsBatch.mockResolvedValue([{ id: 'entra-unused', name: 'Unused' }]);
+
+      await syncUserEntraGroupMemberships(user, 'fake-token');
+
+      const left = await Group.findOne({ idOnTheSource: 'entra-left' }).lean();
+      expect(left.memberIds).not.toContain(userEntraId);
+      expect(await Group.countDocuments({ idOnTheSource: 'entra-unused' })).toBe(0);
+    });
+
+    it('creates missing groups when librechat.yaml turns the setting off', async () => {
+      getUserEntraGroups.mockResolvedValue(['entra-unused']);
+      getEntraGroupDetailsBatch.mockResolvedValue([{ id: 'entra-unused', name: 'Unused' }]);
+      const appConfig = { config: { permissions: { syncOnlyExistingEntraGroups: false } } };
+
+      await syncUserEntraGroupMemberships(user, 'fake-token', null, appConfig);
+
+      const created = await Group.findOne({ idOnTheSource: 'entra-unused' }).lean();
+      expect(created.memberIds).toContain(userEntraId);
+    });
+  });
+
+  it('skips missing groups when only librechat.yaml enables the setting', async () => {
+    const { getEntraGroupDetailsBatch } = require('~/server/services/GraphApiService');
+    getUserEntraGroups.mockResolvedValue(['entra-unused']);
+    getEntraGroupDetailsBatch.mockResolvedValue([{ id: 'entra-unused', name: 'Unused' }]);
+    const appConfig = { config: { permissions: { syncOnlyExistingEntraGroups: true } } };
+
+    await syncUserEntraGroupMemberships(user, 'fake-token', null, appConfig);
+
+    expect(await Group.countDocuments({ idOnTheSource: 'entra-unused' })).toBe(0);
+    getEntraGroupDetailsBatch.mockResolvedValue([]);
+  });
 });
diff --git a/e2e/specs/mock/usage.spec.ts b/e2e/specs/mock/usage.spec.ts
index c77448d2375..85193e1ecb7 100644
--- a/e2e/specs/mock/usage.spec.ts
+++ b/e2e/specs/mock/usage.spec.ts
@@ -283,8 +283,8 @@ test.describe('context usage gauge', () => {
       await page.setViewportSize({ width: viewport.width, height: viewport.height });
       await expect
         .poll(() =>
-          details.evaluate((element) =>
-            getComputedStyle(element).gridTemplateColumns.split(' ').length,
+          details.evaluate(
+            (element) => getComputedStyle(element).gridTemplateColumns.split(' ').length,
           ),
         )
         .toBe(viewport.columns);
@@ -326,8 +326,8 @@ test.describe('context usage gauge', () => {
     await page.setViewportSize({ width: 375, height: 812 });
     await expect
       .poll(() =>
-        details.evaluate((element) =>
-          getComputedStyle(element).gridTemplateColumns.split(' ').length,
+        details.evaluate(
+          (element) => getComputedStyle(element).gridTemplateColumns.split(' ').length,
         ),
       )
       .toBe(1);
diff --git a/librechat.example.yaml b/librechat.example.yaml
index 15215eb6e85..fd68e2320c8 100644
--- a/librechat.example.yaml
+++ b/librechat.example.yaml
@@ -1799,3 +1799,6 @@ endpoints:
 #   maxWriteAttempts: 3 # Integer 1-100, including the first attempt.
 #   leaseTtlMs: 30000 # Integer 1000-600000. Sharing updates on deployments without transactions hold a per-resource lease this long between renewals.
 #   leaseWaitMs: 3000 # Integer 0-60000. How long an update waits for a contended lease before answering 409.
+#   # Login sync updates only Entra ID groups already in the database instead of creating
+#   # every group the user is in. Unset defers to ENTRA_ID_SYNC_ONLY_EXISTING_GROUPS.
+#   syncOnlyExistingEntraGroups: false
diff --git a/packages/api/src/acl/principals.spec.ts b/packages/api/src/acl/principals.spec.ts
index 4fe55c518e7..dd8c1ecdddc 100644
--- a/packages/api/src/acl/principals.spec.ts
+++ b/packages/api/src/acl/principals.spec.ts
@@ -1,4 +1,4 @@
-import { ensureDirectoryPrincipalUser } from './principals';
+import { ensureDirectoryPrincipalUser, syncsOnlyExistingEntraGroups } from './principals';
 
 const createMethods = () => ({
   findUserBySourceId: jest.fn().mockResolvedValue(null),
@@ -52,3 +52,20 @@ describe('ensureDirectoryPrincipalUser', () => {
     expect(methods.findUserBySourceId).not.toHaveBeenCalled();
   });
 });
+
+describe('syncsOnlyExistingEntraGroups', () => {
+  it('defaults to false when neither setting is present', () => {
+    expect(syncsOnlyExistingEntraGroups(undefined, undefined)).toBe(false);
+  });
+
+  it('falls back to the env flag when the yaml setting is unset', () => {
+    expect(syncsOnlyExistingEntraGroups({ maxWriteAttempts: 3 }, 'true')).toBe(true);
+  });
+
+  it('lets the yaml setting override the env flag', () => {
+    expect(syncsOnlyExistingEntraGroups({ syncOnlyExistingEntraGroups: false }, 'true')).toBe(
+      false,
+    );
+    expect(syncsOnlyExistingEntraGroups({ syncOnlyExistingEntraGroups: true }, 'false')).toBe(true);
+  });
+});
diff --git a/packages/api/src/acl/principals.ts b/packages/api/src/acl/principals.ts
index f91d651148e..d49eb70ad26 100644
--- a/packages/api/src/acl/principals.ts
+++ b/packages/api/src/acl/principals.ts
@@ -1,4 +1,5 @@
-import type { TPrincipal } from 'librechat-data-provider';
+import type { TCustomConfig, TPrincipal } from 'librechat-data-provider';
+import { isEnabled } from '~/utils';
 
 export interface DirectoryPrincipalUser {
   id: string;
@@ -46,3 +47,9 @@ export const ensureDirectoryPrincipalUser = async (
     idOnTheSource: principal.idOnTheSource,
   });
 };
+
+/** `permissions.syncOnlyExistingEntraGroups` in `librechat.yaml` takes precedence over the env flag. */
+export const syncsOnlyExistingEntraGroups = (
+  permissions: TCustomConfig['permissions'],
+  envValue: string | undefined,
+): boolean => permissions?.syncOnlyExistingEntraGroups ?? isEnabled(envValue);
diff --git a/packages/data-provider/src/config.ts b/packages/data-provider/src/config.ts
index 642ebb37e9c..f601f0f8da1 100644
--- a/packages/data-provider/src/config.ts
+++ b/packages/data-provider/src/config.ts
@@ -4126,6 +4126,9 @@ export const configSchema = z.object({
       maxWriteAttempts: permissionWriteAttemptsSchema,
       leaseTtlMs: permissionLeaseTtlSchema,
       leaseWaitMs: permissionLeaseWaitSchema,
+      /** Login sync updates only Entra ID groups already in the database instead of creating
+       * every group the user is in. Unset defers to `ENTRA_ID_SYNC_ONLY_EXISTING_GROUPS`. */
+      syncOnlyExistingEntraGroups: z.boolean().optional(),
     })
     .optional(),
   cache: z.boolean().default(true),