In brief: After AMD accidentally leaked a secret version of its FSR 4 upscaling technology, modders began building workarounds to run it on unsupported graphics cards. Although the early results are promising, further performance testing is needed to determine whether the hack is worthwhile.
A recently released unofficial version of FSR 4 offers enhanced image quality on almost any GPU, including the AMD Radeon RX 6000- and 7000-series and Nvidia's RTX 3000-series. However, the higher performance cost over FSR 3.1 might negate any savings from using upscaling.
Although FSR 4 is competitive against older implementations of DLSS, it only officially supports Radeon 9000 graphics cards, which remain above MSRP several months after launch. FSR 4 requires FP8 computation, which doesn't work on older GPUs, but a recent leak revealed that AMD was developing an INT8-based version, which would work.
After AMD inadvertently released the FSR 4 source code with the latest SDK version, modders quickly compiled INT8-compatible DLL files, first on Linux, then on Windows 11. Tested GPUs include the RX 7900 XTX, 6950 XT, and RTX 3060 Ti.
However, depending on the graphics card, switching to FSR 4 might be counterproductive. Modders estimate that FSR 4 on older Radeon GPUs could roughly triple render times from 0.6 to 1.9 milliseconds compared to FSR 3.1, and quadruple them compared to DLSS 4's transformer model on the RTX 3060 Ti.
Still, early examples demonstrate only minor performance penalties on the RX 7900 XTX running Cyberpunk 2077 while significantly improving image sharpness. In a recent test on Windows 11, FSR 3.1.5 reached approximately 84 frames per second at maximum settings with ray tracing at 1440p, while FSR 4 achieved 79 fps, a roughly 7 fps loss.
In an earlier FP8 emulation experiment on Linux with the same graphics card without ray tracing, FSR 4 performed worse than 3.1 but still better than native rendering. It remains unclear when or if AMD might introduce an official INT8 version of FSR 4, which would likely yield better results, at least on RX 7000 GPUs.
Meanwhile, DLSS is likely the better option for RTX users. An FSR 4 hack would only be potentially worthwhile in games that support FSR 3.1 but not DLSS. If any such titles exist, Optiscaler might be a better solution.