The fourth developer preview of OS X Mavericks has been released for registered developers. The update can be installed directly from the App Store by way of Software Update, and weighs in around 1.5GB, depending on the Mac being installed on.
Currently, Software Update provides the only method of installing OS X Mavericks DP4 onto a Mac, as the Apple Developer Center is currently down for maintenance after a security incident occurred.
Additionally, users who have not visited the App store recently since the 3rd DP release will find that updates to the Mavericks Developer Preview Recovery partition and the Samantha voice are also available.
The final version of OS X Mavericks (10.9) is expected to arrive sometime this fall, and will bring tabbed Finder support, improved multi-monitor use, significant processor and power management improvements, file tagging in the Finder, and much more. Macs with Mavericks compatibility are expected to be much the same as those capable of running Mountain Lion, though that may change before the public release later in the year.