AMD revealed its new Zen 3 architecture and the first batch of next-gen Ryzen 5000 series CPUs, with the company promising support for its new Zen 3 processors on current-gen 500-series motherboards.

AMD has also confirmed that Zen 3 support will be included in the previous-gen 400-series motherboards, with beta firmware for 400-series motherboards arriving sometime in January 2021. Between now and then we'll see motherboard makers pumping out new BIOSes for AMD's new Zen 3 processors.
VideoCardz reports that ComputerBase has been collecting data from major motherboard makers, looking at the AGESA updates for Zen 3 on 500-series motherboards. Support for Zen 3 processors will come with AGESA Combo-AM4 v2 1.0.8.x firmware and optional BIOses with Zen 3 coming soon (v1.0.8.x at least).
MSI has confirmed it will have v1.1.0.0 updates by the end of October, while AGESA upgrades for 400-series motherboards are coming soon -- but there's also confusion there. How? The new Zen 3 processors won't work with flagship X470-based motherboards, but have full support on entry-level A520-series boards for the flagship next-gen Ryzen 9 processors. Alrighty.