For the 400 series with the AMD X470 and AMD B450 chipsets, users will have to wait until January 2021 because motherboard manufacturers will have to develop the BIOS for the Ryzen 5000, and that takes time.
According to Wccftech, the 500 series with the A520, B550 and X570 chipsets already have an AGESA 22.214.171.124 BIOS and will switch to AGESA 126.96.36.199 as soon as the processors are available.
During the official opening speech of “Where Gaming Begins”, CEO Dr. Lisa Su announced the next-generation Ryzen 5000 processors based on the new Zen 3 architecture and compatible with existing AM4 motherboards based on the 500 and 400 series chips, while manufacturers independently confirmed that approximately 300 series motherboards would be compatible with a BETA BIOS.
AMD published a lot of content about the new processors, synthetic and in-game benchmarks, but did not mention much about the support of such CPUs for the 400 series motherboards.
Older chipsets, such as the X370, B350, and A320, will not have support for the Ryzen 5000.