It can be stabilized now that #1269 is fixed, if anyone wants to PR that.

Was done in edf35c6.

The biome api does not work for me in 21w20a. Fix it before removing "stable" on 1.17.

Does it work after 9e521e1?

Imo, we can stabilize api part by part; there is nothing that force us to mark the whole api as stable. We can mark those working parts as stable first