Apple has seeded the fourth beta of iOS 8.3 to developers, close to two weeks after seeding the third iOS 8.3 beta and roughly a month and a half after releasing the first iOS 8.3 beta.
The new build of iOS 8.3 carries the build number 12F5061, and is available to download over-the-air or from Apple's iOS Developer Center. Apple also released Xcode 6.3 beta 4 with Swift 1.2 and an update for the Apple TV beta.