As Alfredo wrote:

For other clients we are using 9.6.6 for a while, and I think it's reasonably stable -- plus, we might finally benefit from the nixpkgs snapshots without all those bespoke overlays and yes, it might eventually fix the llvm shenanigans if the llvm-hs folks released a version of llvm-16 (the two concerns are independent, i.e. upgrading GHC vs upgrading nixpkgs, but of course the former is much simpler if we can upgrade via nix the full env)