This Add-on replaces the original skyboxes of Quake 2 and its expansions for an upscaled version using the Waifu2X image scaling (unlimited.waifu2x.net), as well as applying a minimal amount of manual touches. Each face of the skybox was increased from a resolution of 256x256 to one of 512x512, the same resolution as the skyboxes in Call of the Machine.
Hate to be the one who asks, but is this compatible with the remaster?
Yes. Instructions in the files show you where to put them for both vanilla and rerelease.