compatibility with the next generation of ryzen processors

¿La serie 4000 será compatible con las placas base b400?

I don’t think so every new socket always has small diffrences

Yes, the Ryzen 4000 series will use the AM4 socket and after a BIOS update you can also use a B450 board with Ryzen 4000.

https://www.anandtech.com/show/15807/amd-to-support-zen-3-and-ryzen-4000-cpus-on-b450-and-x470-motherboards

Yes it will support! At first first AMD decided to drop support but then there was a huge backlash in the community and they decided to provide support older chipsets. The problem was that new zen 4 CPUs need a larger BIOS size and it wasn’t there in older chipsets. Now AMD came up with a solution for that.
https://insights.tuxforums.com/amd-zen-3-and-ryzen-4000-cpus-will-be-supported-on-b450-and-x470-motherboards/