Since the AMD FSR 4 INT8 DLL leak, we've known that it's possible to use FSR 4 on older GPU architectures than RDNA 4. Recently, we've actually seen successful use of FSR 4 on AMD's RDNA 2 ...
TL;DR: AMD plans to transition from RDNA to UDNA architecture for its GPUs after the RX 8000 series. UDNA will unify gaming and data center GPUs, with RX 9000 set to use this architecture in Q2 2026, ...