Half-Life: ReSrced is a mod for Half-Life, Opposing Force and Blue Shift that gives the game HD textures upscaled from the original low-res textures. This is accomplished by using state-of-the-art neural networks to upscale the game’s graphics. Combined with detail textures and support for a variety of HD model packs for Half-Life and its expansion packs, ReSrced makes the classic game look sharp and modern while keeping true to the original aesthetic.
To make this possible Half-Life: ReSrced runs on the open-source Xash3D FWGS engine. While it's not as plug-and-play as a regular mod for the Steam version of Half-Life, I have made a step-by-step installation instruction that will make the process quite easy. Believe me, it's well worth the effort.