Apple today seeded the first developer build of OS X 10.10.4 Yosemite to testers. The build is labeled 14E7f and follows today’s supplemental update of OS X 10.10.3 and the first developer beta of iOS 8.4 which includes a brand new Music app and iTunes Radio experience.
Today’s release appears to only be available to registered developers and AppleSeed testers; public beta versions of OS X tend to follow in subsequent build releases. For registered developers and AppleSeed members with the Configuration Utility installed, the pre-release software update should be available through the Mac App Store. Apple says the update focuses on “stability, compatibility, and security of your Mac.”