Install SteamOS on Mac: the free app, 6 steps, and what breaks

SteamOS runs on a Mac as a guest system, not as a replacement for macOS. FX Steam Launcher boots Valve’s signed ARM64 SteamOS image, the build Valve made for its Steam Frame headset, in a lightweight virtual machine. Steam and its big-screen interface run natively on the Mac’s chip inside that VM, and only the game itself gets translated.

That translation happens in layers. Proton handles the Windows side of a game, and a translator called FEX converts x86 code (the instruction set Intel and AMD processors use) into ARM code while the game runs. Graphics go from DirectX to Vulkan inside SteamOS, then out of the VM to a driver on the Mac that turns them into Metal, Apple’s graphics system. On macOS 26 and later the default driver is KosmicKrisp; on macOS 15 it is MoltenVK.

One hands-on test counted six layers between Steam and the Apple hardware, which explains most of the glitches covered below. Apple has notarized the launcher, which also carries a Developer ID signature, and its source code is public on GitHub.

• An Apple silicon Mac. Intel Macs won’t work.
• macOS 15 or later. Newer versions get the faster default graphics driver.
• Free space. Plan on about 20GB to start, plus room for games. The SteamOS image alone is a download of about 4.5GB.
• A Steam account and, ideally, a game controller you can pair over Bluetooth.
• Enough memory for your games. One test suggests 24GB of RAM or more for demanding modern games at higher settings, 16GB for mid-range titles, and 8GB mainly for 2D or older games.

1. Download the latest FX Steam Launcher release as a DMG file from the project’s GitHub page, open it, and drag the app into your Applications folder.
2. Launch the app. On first run it offers to set SteamOS up for you; choose Create New Disk.
3. Answer the setup questions. You pick the SteamOS branch, the Steam client (the Steam Deck client is the default, with the Steam Frame client as the alternative), where the disk is stored, an optional password, and how big the games partition should be. The default disk is 64GB, which is enough for a few games; go larger if you plan to install several big ones.
4. Accept Valve’s SteamOS license and the Steam Subscriber Agreement. The launcher then downloads Valve’s image, checks its signature and writes the virtual disk. You don’t need Docker or other developer tools.
5. While it works, pair your controller in System Settings under Bluetooth.
6. When the login screen appears, sign in with your Steam account. Your library shows up in the Steam Deck layout.

A few settings are worth knowing. The disk is sparse, meaning it only takes up space as games fill it, and a Grow Disk option in Settings adds room later without starting over. Settings opens from the menu bar or with Command and the comma key, and lets you change the virtual screen resolution and the sound setup. Crash reports go to the developer’s own server by default; you can switch that off on first run or in Settings.

Older and mid-tier PC games are the sweet spot. On an M4 Max MacBook Pro, The Witcher 3 ran at 70+ fps at 1080p on high settings, though trees were drawn with a visible glitch. Fallout 4 held a locked 60 fps at 1080p on medium, and the first Red Dead Redemption averaged 70+ fps on medium with some graphical issues. Reports for Left 4 Dead 2 range from an average above 140 fps to more than 200 fps.

The developer’s own figures show how much the Mac-side driver matters. On an M1 Max, the Stellar Blade demo ran at about 29 fps with KosmicKrisp against about 18 fps with MoltenVK. An experimental option called DXMT sends DirectX 11 games straight to Metal and can be far quicker: the title screen of Death’s Door reached about 117 fps with it, compared with about 41 on the default path on that same M1 Max.

DXMT has a catch. While it is switched on, programs inside SteamOS can run code on your Mac with your user rights, so the developer advises enabling it only for games you trust. It is off by default and is set per game through profiles in Settings.

Before you install anything big, check the project’s game stats page, where users log how titles run on their Macs. Helldivers 2, for example, shows a 99.5% launch rate and a median of 55 fps across chips such as the M1 Max, M4 Pro and M5. SteamOS also sorts your library into games known to work and games that might.

• Anti-cheat: any game whose anti-cheat blocks virtual machines will not run at all.
• Newer DirectX 12 features: DirectX 12 support stops short of the latest feature level, and goes even lower on MoltenVK. Games that need those newer features, including Unreal Engine 5 titles, don’t start.
• Big-name failures: in testing, Ghost of Tsushima, Doom Eternal and Marvel’s Spider-Man: Miles Morales failed to launch properly.
• Shader stutter: the first time Metal compiles a new effect, the game hitches for a split second, and after that it is cached. Switching drivers rebuilds those caches, and the first run of a large DirectX 12 game can compile for a long time. The Stellar Blade demo took about 28 minutes on an M1 Max.
• Memory pressure: an earlier test on a 16GB Mac mini showed performance falling off once memory ran short.

Some fixes are the same ones Steam Deck owners use. One tester had to adjust graphics settings in some games and needed a fan-made patch to get the controller working in Psychonauts, and often found answers in threads written by Steam Deck owners who hit the same problem.

If you own an Apple silicon Mac and a pile of Steam games marked as unsupported, it costs nothing to try. Pads that work with macOS appear inside SteamOS under their own names, with rumble, and a DualSense can be passed through whole so Steam Input gets its touchpad, gyro, lightbar and adaptive triggers. Sound goes to your Mac’s current output and follows it when you switch, with surround layouts of up to 12 channels but no Dolby Atmos.

It also makes a decent couch setup. Plug a MacBook into a TV over HDMI, grab a gamepad, and the Steam Deck interface works from the sofa. You can even sideload non-Steam games through the SteamOS Desktop Mode, found under Power in the sidebar.

Keep expectations modest on a MacBook Air or an 8GB Mac. A virtual machine can’t use all of the computer’s power, and every translation layer costs some speed. Closing the window shuts SteamOS down in a few seconds or suspends it in memory, but that paused game lives only in memory. Quit the launcher or turn the Mac off and the session is gone.

If FX Steam Launcher isn’t for you, there are other routes. NotProton turns on Steam Play inside the regular Mac Steam app and runs Windows games through CrossOver, with no separate SteamOS install, while UTM 5 added DirectX 11 and 12 acceleration for full Windows 11 virtual machines.