They are doing things differently this time. They've been releasing AGESA 1.0.0.8 since late August and that has initial support Zen 3. And at launch x570 and b550 will get AGESA 1.1.0.0 update which should have full support for Zen 3.
But the fact is there is always optimizations to be found with new releases. So you will likely get frequent BIOS updates at the start again. One thing that will leviate it this time though is that the IO die will be same as with Zen 2.
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You don't have to upgrade if you don't want to. But AGESA updates have usually given support to new things. My work comps x370 board was stable from the launch and I only recently(first time since 2017 I think) updated the BIOS on it because I changed it's memory setup.