Apple has seeded the OS X Yosemite beta 6 to developers and public beta testers, just after releasing the fifth beta of OS X 10.10.4 beta and nearly two months after rolling out the first OS X 10.10.4 Yosemite beta. Follwing the early April release of OS X 10.10.3, whiich included the new Photos for OS X app, Apple was been testing OS X 10.10.4 since mid-April. Now that with the new beta build 14E36b, you can download it through the Software Update style in the Mac App Store or via the Mac Developer Center.
Nevertheless, the OS X 10.10.3 brought with it several consumer-facing changes including the new Photos app for OS X, a redesigned emoji picker, and diversified emoji. But with this new update of OS X 10.10.4 appears to be an incremental one that only brings performance enhancements and bug fixes.
Although, OS X 10.10.4 betas however have not included outward facing design changes or feature additions, but with the fourth beta seeded a significant behind the scenes update that may improve networking performance for users who have experienced issues with OS X Yosemite. Later it was fixed, and removed in favor of the older bug-free mDNSresponder.
No idea on when Apple planning to release OS X 10.10.4 to public, but the fact that it received six betas, suggests that we are nearing the end of the beta stage of testing, and possibly could see a public release of OS X 10.10.4 Yosemite on June 30. Same time when Apple plans to roll out iOS 8.4 with the new Music app and Apple streaming Music service.