Apple has released iOS 8.4 beta 4 for developers, build version 12H4125a, available for iPhone, iPad and iPod touch.
Expect more bug fixes and improvements in this build. How many more betas will we see before the final is released? iOS 8.4 beta 3 was released nearly a month ago.
Yesterday Apple released iOS 9 beta 1 and watchOS 2 beta for developers, immediately after the WWDC keynote.