updated 10:12 am EDT, Fri May 2, 2014
Release notes appear to finalize changes
Apple is seeding a new internal build of OS X 10.9.3 to its workers, 13D57, sources say. While there don't appear to be any major changes since the last public beta, the new code is the first to include formal release notes, detailing exactly what v10.9.3 is meant to fix. Release notes are typically a sign that Apple is on the verge of launching an OS X update.
The notes mention "improved 4K display support" on 2013 models of the Mac Pro and 15-inch MacBook Pro, as well as restoring USB contact and calendar sync between Macs and iOS devices. The software also includes Safari 7.0.3, and improvements to VPN reliability when using IPsec.