Apple today seeded the first build of OS X 10.9.5 to developers, one month after releasing OS X 10.9.4 to the public. The new beta is available through the Software Update mechanism in the Mac App Store and through the Mac Dev Center. The beta has a build number of 13F7.
It is unclear what improvements the 10.9.5 update will bring to Mavericks, but it is likely to include bug fixes and stability enhancements. Apple is asking developers to focus on USB, USB Smart Cards, Graphics, and Safari.
Along with working on improvements to Mavericks, Apple is also beta testing OS X Yosemite, which is due to be released in the fall. The last Mavericks update, 10.9.4, added several Wi-Fi fixes and improved wake from sleep reliability.
Article Link: Apple Seeds First OS X Mavericks 10.9.5 Beta to Developers