Although, Apple rarely launches ".1" beta builds of its mobile OS, iOS 9.2.1 Beta is said to be a minor update featuring bug fixes, under-the-hood improvements, as well as addressing some issues with Mobile Device Management on the recently released iOS 9.2, which apparently don't let apps to fully finish their installation process.
iOS 9.2.1 Beta is now available through Software Update or via iOS Dev Center for registered developers.