Apple seeded a new build of OS X 10.9.4 (build 13E19) to developers on Thursday, just a week after their seed of the second beta of 10.9.4. Apple is asking developers to focus on Graphics Drivers, Bluetooth, Audio Drivers, Finder, App Store, and Safari.
The build is available to developers via the “Update” tab in the Mac App Store, and can also be downloaded in the Mac Developer Center.