I googled AOC U2870 and it came back as 4k. But an easy way to confirm is by right clicking on your desktop then selecting “display settings” then scrolling to “resolution” and seeing what the highest resolultion is - its usually the one that says “(Recommended)” next to the resolution. If it says 3840 x 2160 then you have a 4k display. Also while you are there let us know if you are running 100% or 125% or 150% scaling.