As noted by 9to5Mac, Apple today seeded build 12E55 of OS X 10.8.4 to developers. The release comes nine days after the previous build 12E52 and marks the eighth beta iteration of OS X 10.8.4.
The update is available through the software update tool in the Mac App Store and Apple's Developer Page.
Article Link: OS X 10.8.4 Build 12E55 Seeded to Developers