9.8.1 can't be bootstrapped using 9.6.3 due to erroneous constraints in hadrian
Summary
Hadrian released with 9.8.1 has the following constraint: Cabal >= 3.2 && < 3.9
. This prevents bootstrapping with GHC 9.6.3 (assuming you rely on core packages). To my knowledge, GHC 9.8.1 should be bootstrappable using both the 9.4 and 9.6 series.
(We build hadrian manually via Setup.hs for nixpkgs, so we use the core packages provided by the bootstrapping compiler, in this case 9.6.3 (from the aarch64-linux deb10 bindist.)