updated 02:25 pm EDT, Thu August 7, 2014
Thunderbolt added to listing of testing areas
Apple has begun distributing a new beta of OS X 10.9.5 to developers, available via the Mac App Store or the Mac Developer Center. The code is listed as build 13F12. In addition to Safari, graphics, and USB/USB smart card issues highlighted in the first beta, Apple is now also asking users to test out Thunderbolt connections.
Once it's finished, v10.9.5 will likely be the last major update for Mavericks. OS X Yosemite should launch as a free update in the next two or three months, leaving Apple little reason to support legacy software.