An authenticator app provides one-time codes as a second factor. The codes are generated from a secret key, the so-called seed, which produces a new code every 30 seconds. Microsoft Authenticator can create a cloud backup of that seed, which you can restore on a new device, for example. From January 2027, though, that no longer works on Android with personal Microsoft accounts.
Microsoft added this to a support article about Authenticator backups. On iOS nothing changes, the backup goes to iCloud. It can only be restored on the same type of device, though, so an iOS backup won't work on Android and vice versa.
Android: Google One instead of a Microsoft account
Until now, Android users could flip the "Cloud Backup" switch in the settings and pick a personal Microsoft account as the target. That still works for the moment, but a notice in the app already points to the change. That same account is also where the recovery keys for BitLocker encryption on your PCs can be stored.
Google One is meant to step in instead. Microsoft recommends opening the Google One app, going to "Back up" and "More device data", and selecting "Microsoft Authenticator". Google One then stores the app's settings and data from the outside in its own cloud storage. If you want to switch the recovery account, you first have to delete existing backups: turn Cloud Backup off once, confirm the deletion with "OK", and choose the account switch when you turn it back on. That appears to refer to the app's internal backup to a Microsoft account, which stays supported until the end of the year. How the app will work with Google One in detail isn't something Microsoft explains yet.
The Authenticator keeps shrinking
The move fits a pattern. In summer 2025, Microsoft already removed the password manager from the Authenticator, and it now lives in the Chromium-based Edge browser. If you use the Authenticator on Android, check where your backup lives before the year ends and move it in good time.