Apple today seeded build 13C48 of OS X 10.9.2 to developers, marking the fourth beta iteration of 10.9.2. The release comes a week after the third OS X 10.9.2 beta, build 13C44, and a little over a month after the first OS X 10.9.2 beta.
The update is available to registered developers through the Software Update mechanism in the Mac App Store as well as through the Mac Dev Center.
Apple continues to ask developers to focus on mail, messages, graphics drivers, VoiceOver, VPN, and SMB2. Earlier betas of OS X 10.9.2 began allowing Mac users to block people on iMessage and FaceTime, as can be done in iOS 7, and also introduced FaceTime Audio.