Preview at WWDC likely in June, followed by September launch.
Apple Seeds Fifth OS X 10.10.3 Yosemite Beta to Developers, Public Beta Testers
The new beta, build 14D113c, is available for registered developers through the Software Update mechanism in the Mac App Store and through the Mac Dev Center. Yosemite Recovery Update 3.0 is also available.
With today's update, Apple has continued polishing the Photos for OS X app, and there are just two remaining known issues with the software, including an issue with favorites and a problem with missing thumbnails when restoring an Aperture-upgraded Photos library with Time Machine.
Earlier betas of OS X 10.10.3 have brought several new features to Yosemite, including the new Photos for OS X app. Designed to integrate with iCloud Photo Library, Photos for OS X is a replacement for both iPhoto and Aperture and is on track to see an early 2015 public launch. Reviews have suggested that while Photos is a suitable replacement for iPhoto, with more advanced tools and performance optimizations, it may leave professional users disappointed.
Along with the new Photos for OS X app, the first two OS X 10.10.3 betas introduced a redesigned emoji picker that consolidates emoji into a single page with clear labels, new diversified emoji and emoji skin tone modifiers, new flag emoji and updated emoji for the iPhone, iMac, and Apple Watch, and support for Google 2-step verification when setting up accounts in System Preferences.