Although iOS 8.2 is still in beta, Apple does not waste time in releasing iOS 8.3 beta 1 to developers for the iPhone, iPad and iPod touch, issued a couple minutes ago. This update does not seem proposed OTA (in the device settings), but can also be found on the Apple developers’ page. The size of iPhone 6 Plus is 2.36 GB and it will go through iTunes or Xcode in order to be installed.
iOS 8.2 has been designed to support the Apple Watch, expected in April. It is not yet known what Apple has planned for iOS 8.3, but the manufacturer clearly expected a long development for this update. In comparison, iOS 8.2 is in development since last November and it is still not available for everyone.
The list of new proposed by Apple does not allow developers to find out more. The changes are bugs or undisclosed information to developers: iOS apps for extensions must move to 64 bit, for example.
Furthermore iOS 8.3, Apple also released a new beta version of Xcode development tool for developers. On this side, novelties primarily concern Swift, the new builder programming language.