I just launched the HiDPI UI and it's kind of crazy large. On a retina MacBook Pro, a Sharp 4K and even a retina iMac with higher setting than default, the menu bars and icons consume too much space. See attached screenshot – keep in mind that this is a 32-inch screen.

You can also see that the resolution isn't as sharp as the OS X UI so I don't think it's working right

I'm running a 4K screen on a Mac Pro (late 2013), and have the same issue. The retina scaling does not work. Would really like to se this fixed.

Yes, we are aware of this issue. Convincing OSX to let Houdini have free reign over the pixels on a retina display is not as easy as one might expect. For now you'll just have to live with the jaggies. Or you can change your System Preferences->Display->Resolution->Scaled->Most Space. But then you might need a magnifying glass for some of your other apps (though I personally prefer the “extra” real estate this setting gives me).

Mark