The latest build appears to contain only minor backend changes, with Apple asking developers to focus on the same areas.
In the previous Developer Preview, accompanying release notes suggested changes were made to bring support for iCloud Keychain. That release contained known issues with graphics, including switching views in the Maps app, as well as file handling in Aperture and Photoshop.
Mavericks launches this fall with a host of improvements and new features, including Finder tabs, Maps, App Nap and Compressed Memory, among others.
Developers can download the the fourth beta version of Mavericks through the Mac App Store.