This version of XashXT is intended to be used with Xash3D v0.98, build 3598. It fixes compatibility issues of 3rd revision of XashXT with 3598. DO NOT USE rev. 4 with any other build except 3598! Press "Read more..." for details.
So, this version got some minor errors fixed, mostly it's about compatibility with build 3598. As the revision 3, it has support of free texture coordinates and seamless tiling on studiomodels. Use new studiomdl.exe from devkit\tools with $fixedcoords or $freecoords parameters (like the commonly used $cliptotextures parameter) to compile such models (but they will work properly only with Xash3D, not with GoldSrc).
$fixedcoords is used for texture coordinates to be multiplied by constant (1.0f/32758.0f instead of ptexture->width or ptexture->height). This allows to have good texture positioning's accuracy without need to be attached to texture size's parameters.
$freecoords (or $freecords) is used to get seamless tiling on studiomodels. With this parameter textures on a model will not be clamped by their borders. It also allows to compile models with textures more than 512x512 pixels.
Also this revision of XashXT correctly supports new experimental Unkle Mike's version of VHLT compilers, which allow to adjust lightmap's size and add some other new features. Check this thread for details (in russian):
VHLT compilers included in XashXT's tools are still old, but have a planes' hashing enabled in HLCSG, which is speeding up the process noticeably.
Also Revision 4 is fixing the loading/unloading of resources, which should help to avoid some problems, for example, with changing of video resolution while playing a game.
P. S. Due to problems of compatibility you still have to wait another build of XashXT which will work properly with latest v0.99 of Xash3D Engine.
P. P. S. XashXT's assets have to be placed as a mod inside a main game directory, so you also need to have properly preinstalled Xash3D build 3598 with corresponding resources of Half-Life, otherwise things will not work as intended.