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

First, protect the game's local saves. A compatibility-tool change can rebuild its Windows-like environment, known as a prefix.

1. Select the game in your library.
2. Open the gear or settings icon, then Properties.
3. Go to Compatibility.
4. Tick "Force the use of a specific Steam Play compatibility tool".
5. Choose Proton Experimental from the dropdown.

Use Proton Experimental per game. Do not force it across your whole library.

When you should not use it

Keep changes per game. A build that fixes one title can break another. A per-game selection keeps unrelated games on their existing builds.

Leave a working game alone unless you want a specific fix or feature. A newer build is not automatically better. FSR 4.1 may be a reason to test Experimental; the version number alone is not.

Allow time to test. If people are coming over to play a particular game, keep its working configuration until you have time to check a change and recover from a regression.

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.

Protect local saves before switching Proton versions

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`. Keep a separate backup before changing the prefix, especially for games without reliable cloud saves.

Practical version:

• Check that Steam Cloud has finished syncing; support for the feature alone does not confirm your latest save is uploaded.
• Games without cloud saves, or with mods installed into the prefix, are the ones to back up first.
• In Desktop Mode, close the game and copy its folder inside `steamapps/compatdata/` to a separate backup location before switching.

Uninstalling can also remove the prefix. Re-downloading game files does not recover unsynced local saves.

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 the game still fails, do not assume the prefix is the cause. Check the game's current compatibility notes and verify its files before attempting a reset. If title-specific troubleshooting calls for rebuilding the prefix, preserve a separate copy of its saves and mods first. Deleting it can permanently remove data that was never synced or backed up.