This is incredible, bravo Valve.
Valve seems to have been working away at reducing its dependence on Windows for the last few years. While the Steam Machine and SteamOS initiatives seemed to have not gone anywhere at first (with the latter, especially, not getting many major AAA releases, owing to it being based on Linux), it appears as though the company has been toiling away silently to bridge that gap in available games.
The result? Proton, a new compatibility layer for Linux (including SteamOS), that will let you run Windows games with no Linux versions directly on the system from the Steam client- complete, with support for every controller Steam supports (DualShock 4, Xbox One controller, Nintendo Switch Pro controller, Steam controller), better full screen support, support for SteamWorks and OpenVR, support for Vulkan (with DirectX 11 and 12 implementations being based in Vulkan, for better performance), and better performance for multi-threaded games than on Wine, a Windows compatibility layer for Linux which has been the most popular one in the past (and which Proton seems to be based on).
For now, the feature is in beta and will support limited games (you can find the full list of these games below), but over time, it should be available to everyone and for most games. I’m not much of a Valve fan myself, but I have to laud them for just how audacious and ambitious this initiative seems to be. Hopefully they stick with it in the long run, and don’t lose interest in it.