Ubisoft is pushing out a gigantic patch for Rainbow Six: Siege, with the non-4K update coming in at 26GB, while the 4K update is a massive 42GB.
The team has said that the new patch includes a new baseline that will be the foundation for all future RS:S patches, with the development team replacing countless data forges (the compressed archives that include all of the other files). Future patches shouldn't be as big, but up to 42GB is just MAMMOTH.
Ubisoft is including multiple texture optimizations for Rainbow Six: Siege on the PC, with tweaks made to the texture quality of each level of graphics setting. There's also improved character textures and environmental texture quality, too. The team explains: "Environment textures take up ~60% of available VRAM, and without making the Ultra HD pack unusable by anyone but those with the most powerful builds, the upgraded environment textures did not fit into the Ultra HD pack. Now that we have streamlined the way data and textures are handled, we are able to include these upgrades in the Ultra HD pack, and make it accessible by players that meet the 6GB VRAM minimum requirement".