It's well known that the PS5 will have a certain degree of backward compatibility. However, for now, this only applies to the PS4 and not, as previously assumed, to all previous PlayStation consoles.
Rumors about it keep circulating, including these days (via), where this is presented as an unequivocal fact. However, looking back at official statements from Sony regarding the PS5, it was never mentioned that this would actually be the case. It was perhaps vaguely stated at some point that full backward compatibility was the goal, but without any guarantee or even confirmation.
The main problem here is likely the differing system architectures, which will probably prevent universal compatibility with the PS5. Sony will have to take some detours if they truly want to fully implement this feature. Only the PS4 and PS5 share a similar architecture.
Current surveys This also shows that backward compatibility isn't actually that popular with players. It only ranks fourth (3rd) in terms of desired features, and even then, it seems to refer more to the PS4 and not older consoles.
It remains to be seen to what extent Sony will enable backward compatibility on the PS5. Information on this is expected at the rumored PS5 event in February.
