On Oct. 7, 2026, Valve shipped a Steam Preview/Beta client update that made Proton the default for Windows binaries registered as non-Steam games. The same update fixed two separate problems: a launch failure after changing a non-Steam game’s Target binary through Browse, and a case where Steam’s Stop button failed to close a game launched by an external tool. (Valve’s release notes; BetaNews reported the year for the update date)
Which entries get Proton by default?
Valve’s change applies to Windows binaries registered in the Steam library as non-Steam games. Proton is the compatibility layer Steam uses to run Windows software on Linux. The change sets that layer as the default for the specified entries in the Preview/Beta client.
The manual Proton step
Before the change, users had to configure Proton manually for Windows games added to Steam as non-Steam games, Geeknetic reported. Mii beta’s October 2021 tutorial demonstrates the earlier sequence: enable Steam Play compatibility, add an executable to the library, then select Proton in the game’s Compatibility settings.
Two other fixes for non-Steam games
The update also addressed two distinct client problems. One fix covers a non-Steam game that failed to launch after its Target binary was changed using Browse. The other addresses Steam’s Stop button failing to close a non-Steam game launched by an external tool.
Proton by default is not a compatibility result
Automatic selection removes the manual runtime choice from this setup path; it does not determine whether a particular game will run correctly. ProtonDB describes Proton compatibility as inconsistent and collects community reports and workarounds, which can help when checking an individual title.
