The latest OS X 10.9.4 Mavericks build 13E16 comes two weeks after the first beta was released at the end of May.
Mirroring the OS X 10.9.3 betas, Apple asks developers to focus on Graphics Drivers and Safari, but adds in extra areas of interest in Bluetooth, Audio Drivers, Finder and the App Store.
In the previous seed of Apple's upcoming Mavericks maintenance update, product identifiers pointing to unknown iMac models were discovered in code regarding power management utilities. iMac identifiers "iMac15,1" and "iMac15,n" suggest Apple is preparing to debut at least two next-generation all-in-ones in the near future. Current iMacs hold the "14,1," "14,2," and "14.3" designations.
As for the Safari 6.1.5 seed, Apple's release notes request testers to focus on general website compatibility and extension compatibility.
In addition, the company also seeded the latest OS X Server builds with support for OS X 10.9.4. The new build does not appear to hold any major changes.
Developers can download the latest builds via Apple's Developer Portal or Software Update.