Apple today released a new version of the iTunes 12 beta for both developers and OS X Yosemite beta testers, following yesterday's iOS 8 Golden Master release. Yesterday, users reported having difficulties installing the iOS 8 GM from Yosemite with the iTunes 12 beta, and this update may fix the issue.
First introduced in July, iTunes 12 includes an "elegant new design" that also includes support for several iOS 8/Yosemite features including Family Sharing.
iTunes 12 also includes improved playlists, a redesigned Info Window, and a new icon. iTunes 12 and OS X Yosemite remain in a beta testing phase, with a public release for the software expected this fall, possibly in October.