Proton is a compatibility layer for Windows games to run on Linux-based operating systems.[1] Proton is developed by Valve in cooperation with developers from CodeWeavers.[2] It is a collection of software and libraries combined with a patched version of Wine to improve performance and compatibility with Windows games. Proton is designed for integration into the Steam client as "Steam Play".[3] It is officially distributed through the client, although third-party forks can be manually installed.
Proton was initially released on 21 August 2018.[4] Upon release, Valve announced a list of 27 games that were tested and certified to perform like their native Windows counterparts without requiring end-user tweaking. These include Doom (2016), Quake, and Final Fantasy VI.[5][6][7][8]
Proton incorporates several libraries that improve 3D performance. These include Direct3D-to-Vulkan translation layers, namely DXVK for Direct3D 9, 10 and 11, and VKD3D-Proton for Direct3D 12. A separate library known as D9VK handled Direct3D 9 support until it was merged into DXVK in December 2019.[9]
Being a fork of Wine, Proton maintains very similar compatibility with Windows applications as its upstream counterpart. In addition to the official list of compatible games, many other Windows games are compatible,[10] albeit unofficially, with Proton. The user can optionally force use of Proton for a specific game, even if a Linux version already exists.[11] This may be done when a game's official Linux support is lacking or possibly not stable.
ProtonDB is an unofficial community website that collects and displays crowdsourced data describing the compatibility of a given title with Proton, on a rating scale from "Borked" to "Platinum".[12][13][14] The site is inspired by the WineHQ AppDB, which also collects and displays crowdsourced compatibility reports and uses a similar rating system.
Valve has released eight major versions of Proton. The versioning scheme refers to the upstream Wine version it's based on, with an appended patch number.[15]
Proton generally lags behind its upstream Wine base by several releases. Unofficial forks, such as Proton GE,[16] have been created to rebase Proton on recent Wine versions, which may improve compatibility with games over the official release, and sometimes hurt it.[17]
In December 2020, Valve released Proton Experimental, a perpetual beta branch of Proton that incorporates new features and bug fixes quicker than regular releases,[18] which are eventually included in a regular release.[19]
The Steam Deck uses Proton to increase software title compatibility.[20]
