Latest FSR 4 source code 'leak' lets you run AMD's AI upscaling tech on nearly any GPU — no Linux required

The latest version of AMD's FidelityFX, typically known as FSR 4, delivers a markedly superior result to FSR 3, making it a big win for those who can run it. But that privileged group is limited to folks with AMD Radeon RX 9000 series GPUs based on the company's RDNA 4 architecture. Or is it? As it turns out, you can actually run FSR 4 on nearly any GPU, thanks to AMD itself leaking the source code last month.

Strictly speaking, this isn't exactly 'new' news. As far back as June of this year, people were hacking FSR4 onto last-generation Radeon RX 7000 GPUs, but that trick was fragile and required Linux. Today's method is quite easy and should, in theory, work on virtually any modern GPU in the vast majority of DirectX 12, DirectX 11, and Vulkan games. We'll get to the specifics in a moment, but we should explain exactly what's going on here.

When AMD open-sourced the FSR SDK, including FSR 4, it mistakenly published the full source of FSR 4, not just the SDK portion of it. That meant that anyone could take the FSR 4 code and do whatever they wanted with it, because the source was published under a highly permissive MIT license. Notably, alongside the FP8 version of FSR 4 — that is, the standard version that the Radeon RX 9000 cards normally use — there was also a version built to use the INT8 datatype. INT8 is supported on virtually all modern GPUs, so it is much more compatible.

That was a source release, so it took some hero to come along and compile the source into a binary form that gamers could actually use. That hero turns out to be /u/AthleteDependent926 on Reddit, who provided the compiled DLL file that users can simply drop into games with FSR 3 support to enable FSR 4.

It takes a bit of doing; in our testing, simply swapping the files won't enable FSR 4 the way you might do with DLSS. However, using the OptiScaler mod, you can specifically select FSR 4.0.2 in the mod's UI.

OptiScaler is a multi-game mod similar to something like ReShade or Special K. Install OptiScaler to the game's executable directory, run the "setup_windows.bat" or "setup_linux.sh" depending on your operating system, and then replace the "amd_fidelityfx_upscaler_dx12.dll" with the one from /u/AthleteDependent926's Reddit post. After doing so, launch your game, press Insert to open the OptiScaler UI, select "FSR 3.X" as your upscaler, and then in the "FFX Settings," select FSR 4.0.2. It's a little unintuitive, but it absolutely works.

How do I know? Well, I tested it. First, on a Radeon RX 7800 XT connected to a 4K display, and then on a Ryzen AI Max+ 395's integrated Radeon 8060S connected to a 1440p display. In both cases, performance is a little rough; we saw about 4.1 ms to upscale to 4K on the RX 7800 XT, while the Radeon 8060S takes about 2.3 ms to upscale to 1440p. For those unfamiliar with frame times, 60 FPS equates to a frame time of 16.7 ms. Tacking on an extra 4.1ms for the upscale drops you from 60 to about 48 FPS, but we didn't see that kind of performance from either GPU because we were testing Cyberpunk 2077 in RT Ultra mode on Radeon hardware.

Still, performance remained broadly playable on both GPUs, and the final image quality with FSR 4, while decidedly inferior to DLSS 4, is nonetheless an undeniable step up from FSR 3, and in fact also superior to Intel's XeSS—at least, the DP4a path available to non-Intel GPUs. In Cyberpunk 2077, FSR 4 clearly has fewer artifacts and less aliasing, although it's not flawless; we still saw some trailing on distant objects, and animated textures still throw it for a loop. Only NVIDIA's transformer-based DLSS 4 has resolved those issues.

Of course, some of our problems could be down to the fact that this is a rather hacky way of implementing a fully unsupported upscaler. But regardless, this does seem like a great option to have in the toolbox of Radeon and Arc gamers who don't have access to the latest DLSS models. A great many games have implemented FSR 3 upscaling, and the ability to simply replace that with FSR 4 could be an excellent option if you're already flush with a fine frame rate. Kudos to the enthusiasts and modders who made this trick possible.

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