Valve has introduced a new compatibility layer called FEX to its SteamOS architecture to help Windows games run on Arm-based devices like the Steam Deck and Steam Frame. FEX is a port of the open-source fex-emu project, which translates x86 processor instructions for Arm chips. The tool uses an advanced binary recompiler to support modern x86 extensions and calls graphics libraries like OpenGL and Vulkan to reduce overhead. It also employs code caching to minimise stuttering, according to Steam's developer documentation.

The FEX layer joins Valve's existing Proton tool, which was originally based on the Wine project. Valve engineer Pierre-Loup Griffais told The Verge last year that the company has been funding the lead developer of Fex-emu since the project was in its prototype stage. Griffais noted that Valve anticipated nearly a decade of work was needed before Fex-emu would be robust enough for widespread use.

FEX is designed to work alongside Proton rather than replace it. This layered approach allows Valve to leverage the strengths of both tools to improve compatibility across a wider range of games. The development of FEX has been a long-term effort, with Valve investing in the project from its early days to ensure it meets the demands of gamers running Windows titles on SteamOS.

The addition of FEX is part of Valve's broader push to make SteamOS a viable platform for gaming. By combining Proton and FEX, Valve aims to provide a more flexible and powerful toolkit for running Windows games on Linux. This could lead to better performance and fewer compatibility issues for users of the Steam Deck and Steam Frame.