Proton
Steam Play
Proton is Valve's compatibility layer that lets Windows games run on Steam Deck and other SteamOS devices without the developer making a native version.
Most PC games are made for Windows. Steam Deck and other devices running Valve’s SteamOS are not Windows machines, so to play those games they run them through Proton, which translates what a Windows game asks of the system into something SteamOS can handle.
Proton does not cover everything. Valve’s documentation for developers says that if a game depends on middleware that Proton does not support, or on Windows functions Proton does not fully implement, the game is rated Unsupported. Valve names anti-cheat software specifically: for a game to be rated Verified, its anti-cheat has to work in Proton too.
So a game that runs well on a Windows PC can still be rated Unsupported on Steam Deck if one of its components does not work in Proton. Our explainer on what Steam Deck Verified means covers the ratings in full.
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