Proton Experimental Fixes the CEG Regression and Adds Early 32-Bit OpenXR Support

By Indie Kings | September 26, 2026

Updated September 26, 2026: Valve's Proton Experimental branch has fixed a regression that made CEG-protected games unplayable, fixed Crysis and Crysis Wars on newer AMD CPUs that support CPUID faulting, and added early support for 32-bit OpenXR behind the PROTON_USE_WOW64=1 environment variable on x86.

Verification note: Changes are from the Proton changelog for September 25, 2026, as reported by GamingOnLinux on September 26. Proton Experimental is Valve's testing ground for the next numbered stable release, and the most recent stable is Proton 11.0-2, so anything listed here can change or be reverted before it ships numbered.

Image: Proton. Credit: GamingOnLinux.

The CEG regression, and why it matters

The most consequential line in this changelog is a fix, not a feature: a Proton Experimental regression that made CEG-protected games unplayable.

CEG is Custom Executable Generation, the legacy DRM scheme that wrapped older Windows executables in a check before running them. It is the sort of protection that has always been the most stubborn thing for a compatibility layer to handle, and the significance here is not the feature but the direction of travel. This was a regression in a branch that had worked, meaning a working configuration stopped working and was noticed.

That is worth dwelling on for a specific reason. CEG titles are exactly the category that has historically been the most fragile on Linux, and the reader reaction in the thread on the same page makes the point: a commenter who has repeatedly tried Sniper Elite V2 across Proton versions, with cracks working but generating in-game bugs, reports that it finally worked on Experimental this time.

Being clear about the boundary: a working CEG implementation in a compatibility layer is not a license to circumvent DRM, and our position on that is unchanged. What is notable is purely about engineering, that a branch which had regressed has been fixed and someone with a long record of trying was able to confirm it on a real title.

Crysis and the CPUID faulting problem

The second fix is narrower and more interesting technically. Crysis and Crysis Wars were not playable on some newer AMD CPUs that support CPUID faulting.

CPUID faulting is a mechanism for intercepting and emulating a processor instruction that a program expects to find, used to present a legacy CPU identification surface to software that would otherwise reject the hardware. Modern CPUs, particularly in the RDNA generation and later, do not natively report the instruction behaviour these older titles probe for.

The result is a title that runs perfectly on one CPU generation and flatly refuses to launch on another, which is the worst possible failure mode for a player because nothing in the error message suggests a hardware compatibility problem. Having this fixed in Proton means the workaround lives in the compatibility layer rather than in the user's BIOS, which is the correct place for it.

32-bit OpenXR, and the caveat attached to it

The feature item is early support for 32-bit OpenXR, with an explicit condition attached: it requires PROTON_USE_WOW64=1 on x86.

OpenXR is the cross-vendor standard for VR and AR runtimes, and 32-bit support matters because a large amount of existing VR content is 32-bit. WOW64 is the Windows-on-Windows emulation layer that lets a 64-bit process run 32-bit code, and on x86 that is exactly the path by which a 32-bit OpenXR runtime gets reached.

The word to notice is "early." This is not a finished implementation, and it is not on by default. Anyone planning around it should know that the flag is required and that the feature may change shape before it is enabled without one.

The rest of the update

Four smaller fixes completed the changelog for September 25.

Return to Krondor had rendering corruption, now fixed.
Killer7 had incorrect Japanese text rendering, now fixed.
Hide and Moo! threw an error on quitting, now fixed.

Two of those are worth a second look. Return to Krondor is a late-90s point-and-click adventure that runs through a GOG-era preservation route, and rendering corruption on a title of that vintage is the kind of thing that makes people assume the original is broken rather than the port. Killer7's Japanese text fix is a localisation bug, which is a quietly important category for a compatibility layer, because a game that renders Latin text correctly and kanji incorrectly looks like a deliberate localisation rather than a fault.

Why Experimental matters and what it costs

Proton Experimental is Valve's testing ground for changes that later go into a numbered stable release, with Proton 11.0-2 currently the most recent stable. You install any version by searching "Proton" in your Steam library.

The tradeoff is honest and worth stating plainly. Experimental gets you fixes weeks or months before a numbered release, and in exchange you accept that anything in it can be reverted, and that you are running a build Valve considers untested. For a title that simply does not launch, that trade is usually obvious. For a game you already play fine, there is no reason to move.

This also landed as part of an unusually busy weekend for Valve, with SteamOS 3.9.2 Beta for all devices, a Steam Client Beta update, and SteamOS 0.4.1 Beta for Steam Frame, all covered by GamingOnLinux in the same period. That concentration is itself a signal, since it suggests a push to get several platforms settled ahead of a wider release.

FAQ

What did Proton Experimental fix in the September 25 update?
A regression that made CEG-protected games unplayable, Crysis and Crysis Wars not launching on some newer AMD CPUs that support CPUID faulting, rendering corruption in Return to Krondor, Japanese text rendering in Killer7, and an error on quitting in Hide and Moo!

What is CEG and why does the fix matter?
CEG is Custom Executable Generation, a legacy DRM scheme wrapping older Windows executables. It has been among the most stubborn things for a compatibility layer to handle, and this was a regression in a branch where it had previously worked.

Why did Crysis fail on some newer AMD CPUs?
Those CPUs support CPUID faulting, a mechanism for emulating a legacy processor instruction that older software probes for. Without it, titles that check for that instruction refuse to launch, and the resulting error does not indicate a hardware compatibility problem.

How do I enable 32-bit OpenXR in Proton?
Early support for 32-bit OpenXR was added, and it requires the PROTON_USE_WOW64=1 environment variable on x86. It is early support and not enabled by default.

What is the difference between Proton Experimental and a numbered Proton release?
Proton Experimental is Valve's testing ground for changes that later ship in a numbered stable release, currently Proton 11.0-2. You get fixes earlier in exchange for accepting that changes can be reverted and that the build is untested.

How do I install a specific Proton version?
Search for "Proton" in your Steam library, and the available versions can be selected from there.

Bottom Line

The interesting item in this update is a fix, which is unusual and worth naming. A regression had made CEG-protected games unplayable in a branch where they previously ran, and getting that corrected is the kind of thing that only shows up in compatibility work when someone actually tries a real title on it. A reader with a long record of retrying Sniper Elite V2 across Proton versions reports it finally working here, and one confirmation is not a test suite, but it is a real data point on the most fragile category in the whole Linux gaming stack. The AMD CPUID faulting fix is quietly important for a different reason: without it, a title that refuses to launch on a current CPU gives you an error that points nowhere near the actual cause, and moving the workaround into the compatibility layer is the right home for it. The 32-bit OpenXR support is the feature item, and it arrives gated behind an environment variable and labelled early, so plan around it rather than for it. And the surrounding context matters: this landed in the same weekend as three separate SteamOS and Steam Client betas, which suggests Valve pushing several platforms toward a common release rather than shipping in isolation.

Source: GamingOnLinux, Proton Experimental brings fixes for Crysis, Crysis Wars, CEG-protected games, early support for 32bit OpenXR, by Liam Squires-Hand, September 26, 2026, reporting the Proton changelog for September 25