steamac

# steamac — Valve's official ARM64 SteamOS (the Steam Frame image) in a VM on Apple Silicon

**English** · [Русский](README.ru.md) · [简体中文](README.zh.md)

On macOS 15 (Sequoia), Valve's actual SteamOS for Steam Frame runs in a lightweight VM on
Hypervisor.framework (libkrun) with GPU acceleration via Venus.

```
game (DX9/10/11) ─ DXVK (Proton 11, x86 via FEX) ─ Vulkan
   └─ guest Mesa Venus ─ virtio-gpu (blob, 16K alignment)
        └─ libkrun ─ virglrenderer (Venus) ─ MoltenVK | KosmicKrisp ─ Metal
```

Vulkan on Metal — MoltenVK from the UTM fork (geometry shaders, robustness2) +
`VK_EXT_depth_clip_enable` (PR #2712) + our fixes, by default. KosmicKrisp (Mesa's Vulkan driver on
Metal 4) is an experimental alternative on macOS 26+ (see “Vulkan driver”).

## Requirements

- Apple Silicon Mac, macOS 15+, ~150 GB of free space (the disk image is sparse).
- Xcode 26+ (full installation: its `actool` builds the app icon from an Icon Composer document), Homebrew, rustup.
- KosmicKrisp (optional, alternative Vulkan driver): built only on macOS 26+; `host/kosmickrisp/build.sh`
  installs its Homebrew dependencies (`llvm spirv-llvm-translator spirv-tools vulkan-loader glslang`).
- OrbStack (or Docker with arm64 and `--privileged`): the kernel, Mesa, and disk image are built in Linux containers.
- Homebrew packages: `meson ninja pkg-config dtc xz lld sshpass go` (`go`: license inventory of the bundled gvproxy/desync).
- libepoxy 1.5.10 is built from pinned sources by `host/libepoxy/build.sh`, before virglrenderer and
  libkrun; all three use `MACOSX_DEPLOYMENT_TARGET=15.0`, including on macOS 26/27 build hosts.
  Bundling rejects Mach-O deployment targets above macOS 15.0 (KosmicKrisp alone may require 26.0).

## Building and running

```sh
./build.sh          # Vulkan stack: MoltenVK, virglrenderer, libkrun, launcher, kernel, Mesa, disk
./build.sh dxmt     # DXMT + wmtr host executor and guest payload; then rebuild layer and launcher (below)
./run.sh            # a window with SteamOS
```

Build parts separately: `./build.sh host`, `./build.sh guest`, or the scripts in the table below.
The SteamOS image is downloaded from Valve's servers (a signed RAUC bundle); its signature and
sha256 are verified.

Guest release artifacts have adjacent `.inputs.json` build receipts binding their selected Git
working-tree inputs to their output bytes. Relevant dirty edits invalidate them; unrelated commits
do not. `host/launcher/bundle.sh` refuses missing/stale receipts before modifying the app;
`dist.sh` also validates the receipts and resources inside an existing app before packaging it.
The error names the step to rerun. To refresh guest artifacts without touching an existing SteamOS
disk: `guest/kernel/build.sh` (only when its inputs changed or its receipt is missing),
`scripts/build-image.sh builder rootfs`, `guest/mesa/build.sh`, then
`scripts/build-image.sh initramfs layer`; finally `host/launcher/build.sh`. An unstamped artifact
needs its normal build once; ker