Steamix

Steamix turns a NixOS machine into a Steam machine: it boots straight into Steam’s Gaming Mode (the gamescope-driven Deck UI), and the “Switch to Desktop” button in Steam’s power menu drops you into a regular desktop session — with an icon there to return to Gaming Mode, just like SteamOS.

It is deliberately not Jovian-NixOS. Jovian ships Valve’s full stack (powerbuttond, the vendor gamescope-session, Deck hardware support) and is the right choice for an actual Steam Deck. Steamix instead builds the parts a PC needs: a gamescope session modelled on Valve’s, a session switcher, and a login loop on greetd or SDDM. It is aimed at ordinary PCs used as living-room machines, and leans on upstream nixpkgs’ gamescope and Steam rather than Valve’s patched builds.

Design

Steamix is mechanism only:

• the module touches plain pkgs, plain lib and upstream NixOS options, so it evaluates against a bare nixpkgs;
• all policy (which host, which user, which desktop session) stays with the consumer’s configuration;
• the packages nixpkgs does not have (SteamOS Manager, Decky Loader and the deckyPlugins scope) come from the flake’s overlays.default, and the module’s package options find them there.

Usage

Add the flake and import the module and its overlay:

{
  inputs.steamix = {
    url = "github:arunoruto/steamix";
    inputs.nixpkgs.follows = "nixpkgs";
  };

  # in a NixOS configuration:
  imports = [ inputs.steamix.nixosModules.default ];

  config = {
    nixpkgs.overlays = [ inputs.steamix.overlays.default ];

    steamix = {
      enable = true;
      user = "alice";
      desktopSession = "plasma";
    };
    # the desktop session itself still comes from your own config:
    services.desktopManager.plasma6.enable = true;
  };
}

Requirements and expectations:

• A GPU with working Vulkan (gamescope requires it). AMD is the best-tested family for gamescope — it is what SteamOS runs on.
• The desktop session must be a Wayland session; X11 sessions are out of scope.
• steamix.autoStart (the default) logs steamix.user in without a password prompt, console-style — treat the machine like a game console, not a multi-user workstation. Screen lockers of the desktop session still work once switched.
• Steam itself is unfree; nixpkgs.config.allowUnfree (or an equivalent predicate) must permit it.

HDR, VRR and the performance overlay are on by default and need no configuration — see Options. Resolution, refresh rate and anything else gamescope takes go through steamix.gamescope.args (one list element per argv entry):

steamix.gamescope.args = [
  "--output-width"
  "3840"
  "--output-height"
  "2160"
];

See How it works for the mechanism and its failure modes, Options for the reference, and Hardware setup & tuning for the checklist that makes the machine actually good — nixos-facter, nixos-hardware, gamescope display tuning, controllers. Roadmap is where the project is headed and why.