The Killing Floor-developer Tripwire recently spoke to Wccftech about the rendering resolution of Killing Floor 2 and apparently the game will not run in 4K on the Xbox One X. This because they will prioritise performance over visual quality.
"Killing Floor 2 runs at native 1800p, fixed resolution (no checkerboarding) on Xbox One X. We did experiment with true 4k rendering, but the frame rate drop was a bit too significant. 1800p provides the optimal balance between visual quality and performance in Killing Floor 2."
Dave Elder, Senior Graphics Programmer from Tripwire Interactive continued on the subject by praising the Xbox One X hardware:
"Xbox One X was a very smooth and easy platform to develop for. It took very little engineering effort to get our base Xbox One game running on the Xbox One X. It took maybe 4 hours of programming effort total."