Apple is on point lately with updating Mavericks and today they seeded build 13E28 of OS X 10.9.4 to the public. It’s just been a week after seeding build 13D25 to developer for testing.
As always, the beta build is available through the Software Update in the Mac App Store and through the Mac Dev Center if you are a developer.
It remains unclear what improvements the 10.9.4 build 13E28 update will bring to Mavericks, but it is likely to include bug fixes and stability enhancements to the current build. Apple is asking developers to focus on the following: Graphics Drivers, Bluetooth, Audio Drivers, Finder, App Store, and Safari.