Valve is expanding SteamOS beyond Proton, adding compatibility layers that bring x86 games to Arm hardware and Android APKs into Steam.
According to Ars Technica the first is FEX, Valve’s version of the open-source FEX-Emu project. It translates x86 and x86-64 processor instructions so software written for conventional PCs can run on Arm chips.
FEX uses an advanced binary recompiler that supports modern x86 instruction extensions and can call graphics libraries, including OpenGL and Vulkan, directly. Code caching is intended to reduce the stuttering normally associated with real-time translation.
Valve has been playing the long game here. Valve engineer Pierre-Loup Griffais said last year that the company had funded FEX lead developer Ryan Houdek, even though the technology was little more than a prototype.
Houdek marked the project’s seventh anniversary in November 2025 by crediting Valve with giving him room to build something broader than a proprietary compatibility bodge.
He said: “They trusted me with the responsibility of designing and frameworking the project in a way that it can work long-term; not only for their use cases but also keeping it an open project that anyone can adapt for their own use cases.”
FEX is now being integrated into the Arm-based Steam Frame headset. Valve sees that machine as more than another VR box, with the work potentially opening SteamOS to a much wider collection of Arm hardware.
Griffais said Valve was exploring exactly that possibility. “I think one of the things that we want to do, and that the Frame is kind of paving the way for, is just more general SteamOS for Arm, right?”
Valve’s second compatibility layer is Lepton, an extension of Waydroid designed to run standard Android APKs inside a software container on SteamOS. That is particularly useful for VR, where many games were originally developed for Android-based Meta Quest hardware.
This approach lets developers bring existing mobile VR builds to Steam without creating an entirely new desktop port. Steam metadata analysed this month found 52 of the first 120 titles carrying the “Great on Frame” label were running Android executables through Lepton.
Some of those games represent another change for Steam. Three titles appeared on the storefront without Windows, macOS or Linux versions at all, relying instead on their Android builds when running on Steam Frame.
Valve engineer Jeremy Selan said the system gives VR developers a simpler route onto Valve’s store.
“They are now free to bring those to Steam, and they’ll just work on this device,” he said.
Valve has not ruled out using Lepton for ordinary Android applications and non-VR games, although games remain the priority. With Proton handling Windows software, FEX translating x86 code for Arm, and Lepton swallowing Android APKs, SteamOS is becoming considerably less concerned with what platform software was written for.
