A maximum of the two previous versions, if you set a client upgrade delay and have not yet reached the Scheduled Update date for a more recent version.
Devices automatically upgrade to the most current version, unless:
You set a client upgrade delay, or;
The device is not running a supported operating system. The CrashPlan app will not upgrade until the operating system is upgraded to a supported version. Previous CrashPlan app versions are not supported on devices with unsupported operated systems.