The third beta is out today ahead of the final release expected in July. This third beta brings many bug-fixes and other minor enhancements to ease in porting of software to this next-generation KDE stack.
This beta release also improves the co-instalability support for KDE 4.x libraries and forward compatibility with future versions (such as a theoretical KDE Frameworks 6).
More information on KDE Frameworks 5 Beta 3 can be found via the release announcement at KDE.org. If all goes well, the Frameworks 5 official release will happen on 1 July, per the current KF5 information on the KDE Community Wiki.