The new Beta build is tagged as 15A226f.
The OS X 10.10.5 Beta build is tagged as 14F6a
Step-by-step installation tutorial for anyone
Several under-the-hood improvements landed in the Photos app
Can Apple finally decide ditching 1080p for 4K?
The new Beta has been tagged as build 15A204h
Photos for Mac replaces iPhoto and Aperture
Users can test a new Beta release of Mac OS X 10.10.3
This Beta release has been tagged as 14D127a
The new Beta build is tagged as 14D113c.