We have a mid 2012 Retina MacBook Pro 15" and bought a pair of Samsung U28D590D UHD monitors. 3840x2160 @ 30Hz is possible with the HDMI port. HiDPI and everything just works with 10.9.3. Everything did not just work with a mini-DisplayPort to HDMI adapter. 1920x1080 @ 60Hz was the highest resolution listed with the adapter. 3840x2160 @ 30Hz is possible with the DisplayPort by adding a custom resolution with SwitchResX. Without SwitchResX, the highest resolution listed is 2560x1440 @ 60Hz and HiDPI scaling options are not enabled. We could not find the right setting to use HiDPI with SwitchResX. The monitors have a Picture by Picture feature. We tried to get 3840x2160 @ 60Hz by outputting 1920x2160 @ 60Hz from HDMI and DisplayPort. 1920x2160 @ 60Hz was possible with the DisplayPort. We could not set HDMI to 1920x2160. The monitor has one DisplayPort and two HDMI.