Last month, AMD accidentally made FSR 4 open-source by publishing the entire source code on GitHub, as part of its FidelitySDK. That pushed modders to quickly reverse-engineer how to run FSR 4 on previously incompatible hardware, but the hacks were limited to Linux. That changed just last week when u/AthleteDependent926 on Reddit figured out how to make it work on Windows — we saw a 12-20% decrease in potential performance with it, and today new findings on older RDNA GPUs corroborate our testing.
There are actually three aspects to this story: first, we have an RX 6800 XT that showed a noticeable uptick in visual fidelity at the cost of FPS; secondly, Computer Base tested a bunch of GPUs that saw similar declines in performance; lastly, a Reddit user also tried FSR 4 on their RX 6950 XT and praised its image quality while noting fewer frames achived compared to XeSS. The focal point of the story, though, is the large overhead FSR 4 brings with it, even if it offers a much better-looking image than its predecessor.
The OP on Chiphell modded FSR 4 onto Stellar Blade — a game that only supports FSR 3 natively — using a tweaked DLL that allowed it to work with OptiScaler. The guide to do that was posted later on Reddit by user u/NaM_77, who listed an older driver as a prerequisite. They tested it using their RX 6950 XT and, while no comparison numbers with FSR 3 were provided, the RX 6950 XT still gained about 10% more frames with FSR 4 when tallied against native (TAA) results. Intel's XeSS, on the other hand, had even better performance, but the user highlighted that it was unstable and not as good-looking.
These sentiments are echoed by Computer Base's testing, which didn't use an RDNA 2 GPU. Rather, they pitted an RX 7900 XTX against an RX 9070 XT — AMD's latest flagship purpose-built with FSR 4 in mind. Surprisingly, it still underperformed compared to FSR 3. In Cyberpunk 2077, tested at 4K Ultra settings, the 9070 XT netted 77 FPS using FSR 3.1 and only 74 FPS using FSR 4. More importantly, though, the RDNA 3-based 7900 XTX saw 16% fewer frames in FSR 4 compared to FSR 3.1, but again justified that with markedly better visuals.
All of this to say, FSR 4 seems worth it when it comes to delivering solid image quality, though it still demands significant compute regardless of whatever hardware it's running on. Modders were able to tweak FSR 4 to run INT8 libraries, which themselves have a noticeable discrepancy between each other. FP8 support is only available on RDNA 4, similar to how RDNA 2 GPUs need to fall back on slower instructions like DP4a to run FSR 4 (which explains the missing FPS).
It's important to note that AMD is also working on FSR Redstone as we speak; it's the company's next-gen upscaler designed to work on a myriad of GPUs, including non-AMD ones, which is perhaps why the Red Team hasn't extended FSR 4 support beyond the RX 9000 series yet. Though it's clear that if you're dedicated enough, that's not a hurdle — as long as you can live with worse performance in exchange for sharper fidelity.
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