Apple has released both iOS 8.4.1 and OS X 10.10.5 Betas to the developers:

Apple Seeds First iOS 8.4.1 Beta to Developers
Apple Seeds First OS X 10.10.5 Yosemite Beta to Developers

Apple Seeds First iOS 8.4.1 Beta to Developers

Apple today seeded the first beta of iOS 8.4.1 to registered developers for testing purposes, just two weeks after releasing iOS 8.4 with the new Apple Music service to the public. With iOS 9 already in the works and on track for a fall release, iOS 8.4.1 will likely be the last significant update to iOS 8. Today's beta can be downloaded from the Apple Developer Center.

Read full article @ MacRumors

Apple Seeds First OS X 10.10.5 Yosemite Beta to Developers

Apple today seeded the first beta of OS X 10.10.5 to developers, two weeks after releasing OS X 10.10.4 to the public. Coming just a few months ahead of the public release of OS X 10.11 El Capitan, OS X 10.10.5 may be one of the last significant updates to Yosemite.

Read full article @ MacRumors