Just over two weeks after releasing OS X 10.8.3 build 12D44 to developers, Apple released another beta seed earlier this week, once again listing no known issues. The update is thought to be near completion, and is expected to be released in the very near future.
From Apple’s official seed notice sent to developers:
Build 12D50 (Pre-Release)
This is a pre-release update to OS X Mountain Lion 10.8. To install OS X Mountain Lion Update 10.8.3, you must first download and install the OS X Software Update Seed Configuration Utility. Please refer to the seed note for more details and complete installation instructions.
Developers are once again asked to focus on AirPlay, AirPort, Game Center, Graphics Drivers, and Safari as they test their apps against the new build. The beta is available now through Software Update on Macs that are already running a beta build, as well as for direct download at Apple’s developer site.