When it comes to X1X it means there are times it'll render at higher than 4K and then downsample to whatever resolution the X1X is outputting to. Its is truly glorious on a 4K display. This quote will come back to haunt me, I'm sure, but there were times on Wargames last time I was testing where it was rendering at ~3200p (6K?) internally. The internal render resolution is dictated by the GPU load, so obviously there are no guarantees as to how often it renders at particular resolutions, but essentially we're using 100% GPU all the time.