Steam Machine · Guides
How to Use Proton Experimental on Steam Machine
Summary
Use Proton Experimental on Steam Machine for a specific compatibility or FSR 4.1 reason, switch it per game, and protect saves before changing Proton prefixes.
# How to Use Proton Experimental on Steam Machine
Proton is the compatibility layer that lets Windows games run on SteamOS. Most of the time you never think about it, Steam picks a version and the game launches.
Proton Experimental is the rolling test build of that layer. It gets fixes and new features before they reach stable Proton, which means it is where new capability lands first and where new bugs land first. Both halves matter.
The reason Steam Machine owners care right now
Valve's Steam Machine update says FSR 4.1 on Steam Machine is available through Proton Experimental. The game still needs a supported FSR upscaling implementation. Proton does not add upscaling to a game that has none. Image quality and frame-time cost vary by game and render resolution, so treat this as a per-title experiment rather than a universal performance switch.
Install it
Search for "Proton Experimental" in your Steam library and install it like any other Steam compatibility tool. It updates as a rolling test build, so the version can change between sessions.
Switch a single game to it
- Select the game in your library.
- Open the gear or settings icon, then Properties.
- Go to Compatibility.
- Tick "Force the use of a specific Steam Play compatibility tool".
- Choose Proton Experimental from the dropdown.
Do this per game. There is a global option that forces Experimental for your whole library, and you should not use it, for reasons below.
When you should not use it
This is the part most guides skip.
Do not set it globally. Experimental is a moving target. A build that fixes your one game can break five others you were not thinking about, and you will not connect the two events a week later when something stops launching. Per-game means the blast radius is one game.
Do not use it on a game that already runs well. If a title is stable on the default Proton version Steam selected, switching to Experimental gains you nothing and exposes you to regressions. "It works" is a good reason to leave it alone.
Do not use it right before you need the machine to work. Experimental updates land continuously and without release notes you will read in advance. If you have people coming over to play something specific, that is not the evening to move it onto a test branch.
Be careful with anti-cheat games. Valve's Proton hardware guidance explains that anti-cheat compatibility depends on the game, vendor, and Proton configuration. Experimental changes can break a game that was working, so check the title-specific status before changing versions.
The save file risk nobody mentions
Switching Proton versions can trigger the game's prefix to regenerate.
A prefix is the little synthetic Windows environment Proton builds per game, living in `steamapps/compatdata/` under the game's App ID. If a game stores saves inside that prefix rather than in Steam Cloud, regenerating it can leave those saves behind.
Valve's Proton release notes document a Steam Cloud and new-prefix failure mode where recoverable files can be left in directories containing `corrupted_pfx`. That is why a backup is worth the minute it takes, especially for games without reliable cloud saves.
Practical version:
- Games with working Steam Cloud saves are low risk.
- Games without cloud saves, or with mods installed into the prefix, are the ones to back up first.
- Back up by copying the game's folder inside `steamapps/compatdata/` before you switch. Desktop Mode, file manager, done in a minute.
Uninstalling a game deletes its prefix outright, which is the same risk by a different door. Worth knowing separately.
Switching back
Same path, untick "Force the use of a specific Steam Play compatibility tool", and Steam returns the game to whatever version it picks by default.
If a game broke after you switched and it stays broken after you switch back, the prefix is the likely culprit rather than the Proton version. Delete the game's folder in `steamapps/compatdata/` and launch again to build a fresh one. You will lose anything stored in that prefix, which is why the backup step above exists.
The short version
Use Proton Experimental per game, for a specific reason, when the default is not doing what you need. FSR 4.1 on Steam Machine is currently a good reason. "Newer sounds better" is not.