How iOS 15 Temporary iCloud Storage Preserves App State

Apple introduced temporary iCloud storage in iOS 15 to grant users unlimited, short-term backup capacity to facilitate seamless device upgrades without requiring a paid iCloud plan. This feature preserves the exact configuration state of installed applications by taking a comprehensive snapshot of application sandboxes, user preferences, and local databases, and then restoring that data onto the new device alongside fresh application binaries downloaded from the App Store.

The Temporary Backup Snapshot

When initiating a transfer, iOS creates a targeted device snapshot uploaded to a dedicated, temporary iCloud container valid for up to 21 days. Rather than backing up complete application binaries, the operating system isolates and packages only the data necessary to recreate the application's current environment. This drastically reduces transfer times while preserving fidelity.

Sandbox Container Preservation

Every iOS app operates within a standardized, sandboxed directory structure. Temporary iCloud storage captures the persistent directories within this sandbox:

  • Library/Preferences: Contains the property list (.plist) files managed by UserDefaults. This preserves user-defined settings, flags, theme choices, and configuration switches.
  • Library/Application Support: Stores configuration files, Core Data stores, SQLite databases, and offline content required for the app to function continuously.
  • Documents: Retains user-generated content and essential data exposed to or created by the user.

To optimize transfer efficiency, the system explicitly bypasses the Library/Caches and tmp directories, as these store regenerable assets that are not required to maintain application state.

Decoupling Binaries from Configuration

Temporary iCloud backups do not upload the actual application executable files (.ipa). Instead, the backup records the unique bundle identifier, version metadata, and installation records.

During the restore phase on the new device:

  1. The new device parses the backup manifest and queues the identical application versions for download directly from the App Store.
  2. The operating system creates new, secure sandbox directories for each app.
  3. The temporary iCloud service streams the backed-up sandbox data directly into the corresponding directories before the user launches the application for the first time.

Keychain and Authentication Persistence

State preservation extends beyond local directories to cryptographic tokens and authentication states. Items stored in the iOS Keychain that use appropriate accessibility attributes (such as kSecAttrAccessibleAfterFirstUnlock) are backed up using end-to-end encryption. When the temporary backup is restored using the user's Apple ID and device passcode, these tokens are decrypted and repopulated, allowing most applications to remain logged in without prompting for re-authentication.

Final State Reconstitution

Once the data transfer completes and the app binary finishes installing, the operating system finalizes file permissions and ownership flags within the app container. When the user opens the app on the new device, the execution environment reads the restored configuration files seamlessly, restoring the exact state, preferences, and session data present on the previous device.