AMD FSR 4.1 Leaked Early via Valve's Proton: What We Know So Far

AMD's FSR 4.1 upscaling technology is coming soon, but thanks to an accidental leak by Valve, some PC gamers are getting an early — and unofficial — look at what it can do.

On or around June 22, 2026, Valve inadvertently included AMD's unreleased FSR 4.1 binary files in a Proton Experimental build for Linux/SteamOS gaming . The leaked file, named "FSR 4.1.1 Int8" , contained the key dynamic link library (DLL) amdxcffx64.dll . The presence of the files was first flagged by XR analyst Brad Lynch, who posted screenshots of the traces online, with SteamDB records later confirming the update .

Valve quickly pulled the premature build from the Proton Experimental branch after the leak was discovered . However, this wasn't the first time FSR 4.1 files had slipped out. On Windows, a separate leak had already occurred earlier in the year. Users extracted and shared similar DLL files from AMD's invite-only "Vanguard" Adrenalin 26.3.1 beta driver back in February 2026, allowing Windows users to swap the amdxcffx64.dll in System32 to activate FSR 4.1 in supported titles . By mid-March 2026, AMD had also removed recent FSR 4.1 DLLs from its official download.amd.com directory .

Technical Implementation: INT8 and VKD3D-Proton

The leaked Proton build is labeled "FSR 4.1.1 Int8" , indicating that it uses INT8 (8-bit integer) data conversion for its machine-learning inference pipeline . This is a notable detail because it differs from the FP8 (8-bit floating-point) version. The INT8 variant is broadly compatible with more GPU architectures but can incur a higher performance penalty when running .

On Linux, this implementation works through VKD3D-Proton, the translation layer that routes DirectX 12 calls. This allows the FSR 4.1 DLL to run on RDNA 3 and RDNA 3.5 GPUs under Proton . This follows the same pattern as earlier community tweaks where a leaked version of AMD's FSR 4 was adapted for RDNA 3 hardware .

Reported Performance Gains

Early performance data is limited and should be taken with caution. A single Reddit user reported testing the prematurely released FSR 4.1 files in Stellar Blade and claimed an approximately 8% improvement in frame rate at 1440p compared to earlier FSR versions . It is important to note that this is a single user report on a forum, not a verified benchmark from a reputable reviewer. The claim remains preliminary and unconfirmed.

Official Launch Plans

Despite the leaks, AMD's official release timeline appears solid. Multiple sources report that AMD plans an official FSR 4.1 update in July 2026 for its Radeon RDNA 3-based GPUs (RX 7000 series) . The official release is expected to bring native FSR 4.1 support to over 300 games .

For owners of older hardware, the news is also promising. Reports indicate that support for RDNA 2 (RX 6000 series) is expected in early 2027, though this timeline has not yet been confirmed by an official AMD announcement . On the Linux front, SteamOS developer Pierre-Loup Griffais hinted in an interview with Digital Foundry that FSR 4 on Linux could ship "on the same schedule (as the Windows release)" .