Apple on Thursday seeded OS X 10.8.3 build 12D44 to developers, with the new version coming just two days after the previous 12D43 build was released. From Apple Insider:

It is not clear what changes have been made with the new OS X 10.8.3 beta as people familiar with the previous build say developers are being asked to focus on the same areas. In fact, the release notes are identical to those released alongside build 12D43 on Tuesday.

Thursday's notes also come with the same step-by-step instructions for installing and activating the "OS X Software Update Seed Configuration Utility," which allows developers to download new seeds directly through Software Update in the Mac App Store. The new feature was first introduced in build 12D38 released at the start of December.

Apple seeds new OS X 10.8.3 build two days after previous version's release