While the focus this week is on iOS 9 and OS X 10.11 El Capitan, those won't become available to the public until this fall. In the interim, Apple has new updates for iOS and OS X that remain in testing, patching bugs and issues for each platform.
The fourth beta of iOS 8.4 and the fifth beta of OS X 10.10.4 were both provided to developers on Tuesday, a day after iOS 9 and OS X 10.11 were formally announced. The new build of iOS 8.4 is identified as 12H4125a, while OS X 10.10.4 is build 14E33b.
Apple's iOS 8.4 features a revamped Music application that will presumably feature support for the upcoming Apple Music subscription service. Apple has said that Apple Music will debut on iOS devices, as well as iTunes for Mac and PC, on June 30, which might hint when iOS 8.4 will arrive.
The latest build of iOS 8.4 still has a number of known issues, Apple warned developers on Tuesday, Most of these are associated with the revamped Music app, including bugs that prevent AirPlay streaming, Home Sharing, Genius Mixes, and various issues with iTunes Radio.
While iOS 8.4 will feature a redesigned Music application, such major changes are not expected in OS X 10.10.4, which is expected to be largely for fixing various bugs.