Not just Proton: Getting to know Valve's new SteamOS compatibility layers

Ars Technica details Valve's push to make SteamOS work across more hardware than the Steam Deck ever needed. For the Steam Frame, Valve is leaning on two additional compatibility layers alongside Proton: FEX for x86-on-Arm translation, and Steam Play's broader compatibility plumbing for Windows software.

FEX is based on the open source fex-emu project and acts as a binary recompiler for x86(-64) code running on Arm chips. Valve's documentation says it can route graphics calls through OpenGL and Vulkan and uses code caching to reduce stutter, which matters a lot for game workloads where translation overhead can quickly become a frame-time problem.

The practical takeaway for developers is that Valve is investing in a deeper compatibility stack rather than betting solely on native ports. That should help older PC libraries and Windows-first releases reach more devices, but it also means performance, middleware behavior, and anti-cheat or DRM edge cases will still need testing on translated paths.

Valve has been funding FEX lead developer Ryan Houdek since the project was still a prototype, and Pierre-Loup Griffais has said the company expected years of work before it would be dependable enough for users to trust with their libraries. That long runway suggests Valve sees compatibility as core platform infrastructure, not a short-term launch feature.