Apple today seeded the first test build of OS X 10.9.3 to registered Mac developers



From MacRumors:

The new beta, which has a build number of 13D12, is available through the Software Update mechanism in the Mac App Store as well as through the Mac Dev Center. Apple is currently asking developers to focus on Graphics Drivers and Audio, and there is no word yet on specific fixes and changes included in the update. The last Mavericks update, OS X 10.9.2, added FaceTime Audio, the ability to block iMessage users on the Mac, and a fix for a critical SSL vulnerability.

  Apple Seeds First OS X Mavericks 10.9.3 Beta to Developers