New 21.5-inch Retina 4K models expected.
Apple Releases OS X Mavericks Developer Preview 8
OS X Mavericks, which is expected to be released this fall, includes multiple new features like a tabbed Finder, full screen dual monitor capabilities, Safari improvements, and a new Maps app.
Apple is reportedly targeting a late October launch for OS X Mavericks.
Update: As noted by 9to5Mac, Developer Preview 8 includes an updated version of iTunes 11.1 that adds an option to turn off song change notifications.