Direct support was only for 1920x1080p (which interestingly enough the Dell UP2414Q actually WAS able to scale to fit the screen and run at 60Hz, although it doesn't do simple scaling but interpolation so it's a bit blurry looking from the interpolation).
I have no clue what Apple fans go on about how MS has no clue compared to Apple when getting UHD running on a regular MAC is so tricky and not directly supported in the OS. It took a lot of searching and some hacking and some serious scares along the way though! And most google searches only lead you to partial solutions or talk that it's impossible. OK, wow, actually got my MAC Mini to be able to support 3840x2160 or 1920x1080p HiDPI modes.
