Backed for the current generation of the Xbox One, backward compatibility should probably be on the side of Sony, but not before the release of PlayStation 5.
Backward compatibility is a feature that makes it possible to play back to earlier Generation games on newer consoles. This feature is still a problem with every new generation of consoles.
As for the current generation, Microsoft has a big advantage over Sony. The American company has found a technical way to make it workable Xbox One, so you can play titles from Xbox 360 and even the very first Xbox.
On the other hand, Sony's console users have remained rather low on the entire console generation. But with PlayStation 5, things should change a priori.
Several sources converge that the next Sony console should actually provide a means for backward compatibility. Among other things, this could be done through streaming solutions.
This is also what the reports of Mat Piscatella, who works for the NPD Group, say about the PS5. "I would be surprised if the PlayStation 5 is not backwards compatible with the contents of the PlayStation 4, Sony already has a game streaming service with the PlayStation Now", he explains on ] Interview with GamingBolt [1