Build 12D54 comes just eight days after build 12D50, and like the previous build, contains no known issues or features. Build 12D50 brought only minor changes, and asked developers to focus on testing AirPlay, AirPort, Game Center, Graphics Drivers, and Safari.
9to5Mac notes that the new build contains significant changes to WiFi, but additional changes are unknown. Registered developers can download the update on Apple's Developer Page.
This post originally referred to Build 12D54 as the seventh developer seed of OS X 10.8.3 when it was actually the sixth seed.
Article Link: Apple Seeds Build 12D54 of OS X 10.8.3 to Developers