Not optimized for 4k. There IS a way to fix that with one reg setting and adding this manifest fill to each app folder for apps not optimized, link below. After doing the reg edit any one you add the manifest file to (changing the name) shows normal size for 4k. Shouldn’t have to do it but the world is not perfect. Whining about the mascot is really ridiculous, I actually like it. If you are a snowflake though beware as there is a cartoon ant. Get your safe room ready.
http://pocketnow.com/2016/01/25/hidpi-scalling-in-windows-10