OS X 10.9.3 released
 

Apple has released OS X Mavericks 10.9.3 Update, which brings a pixel-doubled Retina mode to external 4K displays and restores contact and calendar syncing between Mac and iOS devices in iTunes. The Retina mode makes content much sharper, rather than just using all the pixels to create a truly huge desktop. You know where to get it.

http://osnews.com/story/27732/OS_X_10_9_3_released