Apple is releasing new Mavericks betas like clockwork with the last three coming one week apart from each other. Developers can now download the latest Mavericks update, OS X 10.9.3 beta 3 from the Mac Dev Center or via Software Update.
The first OS X 10.9.3 beta added support for a full range of Retina scaling modes for 4k monitors. The other have mostly focused on bug fixes with the latest seed note asking devs to focus on graphics drivers, audio, Safari, and contacts & calendar sync over USB in iTunes.
An iTunes 11.1.6 beta was also released this afternoon to devs that restores the ability to sync contacts and calendars to USB after Apple removed the option in favor of an iCloud-only approach.