SteamOS architecture

SteamOS combines a Linux operating-system base with a controller-first Steam session and compatibility technologies for Windows games.

The diagram is conceptual. Exact component versions and vendor driver paths vary by SteamOS release and hardware.

Graphics and compatibility flow

Native Linux

Windows

D3D 9/10/11

D3D 12

Wayland or X11 presentation

XWayland or Wayland presentation

DRM/KMS in Gaming Mode

nested session

Steam Client / Game Mode

Game build

Vulkan / OpenGL

Proton + Wine

DXVK

VKD3D-Proton

Mesa or vendor graphics driver

Vulkan

Linux kernel DRM/KMS and device drivers

GPU and display

Gamescope Wayland compositor

Host Wayland or X11 compositor

Component responsibilities

ComponentPrimary responsibility
Linux kernel
Scheduling, memory, input, storage, networking, DRM/KMS, and hardware drivers
Mesa
Open graphics drivers and Vulkan/OpenGL userspace implementations for supported hardware
Gamescope
Gaming-session composition, scaling, frame limiting, and display presentation
Wayland/XWayland
Native Wayland protocol support and an X server bridge for X11 game clients
Proton and Wine
Windows API compatibility and Steam integration for Windows game builds
DXVK
Direct3D 9/10/11 translation to Vulkan
VKD3D-Proton
Direct3D 12 translation to Vulkan
KDE Plasma
The graphical desktop used in Desktop Mode
Flatpak
The preferred application delivery path for many Desktop Mode applications

Operating-system and application boundaries

SteamOS 3 uses Arch Linux packages as its base, but Valve ships and updates it as a managed operating-system image. The root filesystem is read-only by default. Disabling that protection or installing base packages with pacman is possible for advanced work, but those changes can conflict with or disappear during later image updates.

Flatpak is the safer persistence boundary for many Desktop Mode applications. Steam Linux Runtime containers separately provide predictable libraries to native Linux games and Proton; they are not a replacement for the host kernel, graphics driver, or per-game Proton prefix.

BoundaryOwnsDoes not own
SteamOS image
Base userspace, system services, desktop, and Valve update state
Per-game Windows registry and files
Steam Linux Runtime
Controlled Linux userspace for a title or compatibility tool
Host kernel and hardware driver
Proton prefix
Per-game Windows-compatible files, registry, and runtime state
The full SteamOS installation
Flatpak
Sandboxed Desktop Mode application and declared data access
Gaming Mode compositor or kernel

Update implications

When diagnosing a regression, record the SteamOS build, update channel, kernel, graphics stack, and selected per-game compatibility tool. A game update, Proton update, runtime update, and SteamOS image update are separate variables even when Steam delivers all of them.

How to verify the active stack

Use Steam's system information and a game's Proton log before assuming which compatibility path is active. A per-game diagnostic guide will be added in the compatibility phase.

Frequently asked questions

Does a Direct3D 12 game pass through DXVK first?
Does a Direct3D 12 game pass through DXVK first?
No. Proton normally uses DXVK for Direct3D 9, 10, and 11, while Direct3D 12 uses VKD3D-Proton. They are parallel translation paths.
Is Gamescope a replacement for Proton?
Is Gamescope a replacement for Proton?
No. Gamescope manages presentation and the gaming session, while Proton provides Windows compatibility services for games that need them.

Sources

Version history

  • 2026-07-15: Phase 3 architecture edition with OS-image, runtime, prefix, and Flatpak boundaries.