This is a 64 bit version. It is not compatible with old mods or old saves. To run old mods, use compatibility mode and run the mod on dedicated server. Use a clean installation - to avoid problems.

Hdr monitors support (nvidia only, 10bit output color) To use set r_useHdrDisplay 1
Physical based camera for automatic exposure (in ldr mode you can disable auto exposition - set r_hdrEVcomp -1.0 )
Improved 1000nit ACES tonemaper for hdr monitors
Screen space pseudo lens flares postprocess effect
OpenGL 4.5-4.6 core profile
Native x64 executable
Compute shaders for gaussian blur
Hi quality precompressed DDS textures for everything (DX11 class hardware, HDR and LDR textureformats, dds cubemaps support, no tga, jpg, png textures now)
Better memory management
Automatic memory allocation for levels and models
Per polygonal weapon hit collision (buggy, disabled)
Restore some Berserker's attack (from re-release)
External hrtf files (use openal soft configuration utility to connect directory with external files)
Uncompressed tangent space vectors for md2 for better lighting quality
Better AMD cards supporting

https://www.moddb.com/mods/quake-2-xp/downloads/quake2xp127-beta2