AMD has officially stated that Ryzen 5000 support for the 400 series chipset will be coming in 2021, but that doesn't appear to be the case anymore. Three companies have shared (so far) that they will support AMD's new Ryzen 5000 series CPUs before 2021, Biostar, Asrock, and Asus. With Asrock already having beta BIOS's ready for the shiny new CPUs.
To ensure compatibility, you'll need a BIOS for your specific B450 motherboard that supports AGESA 1.0.8.1 at the very minimum. This AGESA code enables Ryzen 5000 Renoir compatibility. In order to get the full performance out of your Ryzen 5000 CPU you'll need to make sure your B450 motherboard has a BIOS supporting AGESA 1.1.0.0 or greater.
Biostar has said via Twitter that they will be supporting Ryzen 5000 CPUs coming soon, whether that's before 2021 or after 2021 we are not sure. Regarding Asus, they are more straight forward with the deadline, marking a December release for AGESA 1.1.8.0 BIOS's that will be available for all its 400 series motherboards (not just B450).
Asrock is the strangest of the three though; reportedly Asrock has released beta BIOS's for its entire B450 lineup of boards (no word on X470), but quickly withdrew them from the public eye. AnandTech covered the strange occurrence and they have no idea why the BIOS updates were pulled.
