Valve’s SteamOS Layers Move Beyond Proton With New Linux Compatibility Paths

Valve has spent years building a bridge between Windows PCs and the SteamOS that powers the Steam Deck. That bridge is Proton, a compatibility layer that turns x86 software into code the Deck’s Arm hardware can run. Now the company is adding two new bridges, and one of them is finally ready for prime time.

The Steam Frame headset runs on SteamOS, and getting Windows games onto it required more than Proton could deliver on its own. Valve turned to FEX, a project it has funded since before it had a working product, and to a second layer that remains unnamed in the source material. The combination is what makes the Frame possible. And Valve sees this as the beginning, not the end.

What Proton Already Does

Proton is the older sibling in this family. It is a compatibility layer built on top of Wine, a decades-old project that converts x86 binaries into something Linux can understand. Proton is based on Wine, and it has become a common way to run Windows games on the Steam Deck.

Valve did not invent Proton from scratch. It took an existing tool and made it better. The approach worked well enough that the Deck became a serious gaming machine.

But Proton has limits. That is where FEX comes in.

FEX and the Long Road to Readiness

FEX stands for Fex-emu, an open-source project that emulates x86 processor instructions on an Arm chipset. The project started in 2018 as a small cross-platform emulation effort. It grew quickly, adding features that let it support modern x86 instruction sets.

According to the Fex website, the emulator includes “an advanced binary recompiler that supports all modern extensions of the x86(-64) instruction set.” It also makes calls to graphics libraries like OpenGL and Vulkan to reduce overhead, and it uses “code caching to minimize stuttering as much as possible,” per Steam’s own developer documentation.

Valve’s investment in Fex began before the project had a working prototype. Valve engineer Pierre-Loup Griffais told The Verge last year that the company has been funding Fex lead developer Ryan Houdek since the project was just a prototype. The commitment was early and deep.

Griffais was blunt about the timeline back then. He said close to a decade of work would be needed before Fex-emu would be robust enough for people to rely on it for their libraries. That is a long wait for a compatibility layer, and it reflects the scale of the problem.

Why Valve Funded the Project

The funding relationship is unusual in tech. Most companies invest in open-source projects after the code proves itself. Valve invested before that proof existed. The reason is simple: Valve wanted a path to run x86 software on Arm hardware, and it saw Fex as the best bet.

Houdek thanked Valve publicly for that trust. In November, he marked the seventh anniversary of the project with a note of gratitude. “I want to thank the people from Valve for being here from the start and allowing me to kickstart this project,” he wrote. “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.”

The statement is notable for what it says about Valve’s intentions. The company treated Fex as a long-term investment, not a quick hack. It wanted the project to work for everyone, not just for its own devices.

From Prototype to Integration

The integration is significant. The Steam Frame is a SteamOS-powered device, and it runs Windows software through FEX. That is a practical demonstration of a compatibility layer doing real work in a shipping product.

What Comes Next for SteamOS on Arm

Valve is not stopping at the Frame. Griffais told Rock Paper Shotgun that the company is actively exploring versions of SteamOS for other Arm devices. “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?” he said. “There’s a bunch of devices where you could have a great experience running SteamOS on there, that are currently kind of this adjacent ecosystem that’s just a little bit different. But not really that different, in our opinion.”

The quote points to a broader strategy. Valve sees SteamOS as a platform, not a one-off. The Frame is the test case.

“There’s a bunch of devices where you could have a great experience running SteamOS on there, that are currently kind of this adjacent ecosystem that’s just a little bit different. But not really that different, in our opinion.”

The phrase “adjacent ecosystem” is telling. Valve is not talking about a new market. It is talking about devices that are already out there, with processors that could run SteamOS if the compatibility layers were in place. The Frame proved the concept.

The Open Source Angle

Fex is an open-source project, and Valve has kept it that way. That decision means the work is visible to anyone who wants to check it.

The Road Ahead

Valve has spent a decade building the foundation for SteamOS on Arm. The Frame is the first major milestone, and the company is moving forward. The next step is bringing SteamOS to more devices.

The open-source nature of Fex means the work is available for others to build on. That could accelerate adoption beyond Valve’s own products. The compatibility layers are real, and they are working.

The Steam Frame is the proof that the layers work. The next question is which devices get them next.

The table shows the sequence of events. Fex started as a small project, got early funding, and reached maturity over a decade. The Frame is the proof that the layers work. The next step is bringing SteamOS to more devices.

Arm · FEX · Proton · Steam Deck · SteamOS · Valve