It was usually recommended to lock to inputs anyhow with all the fetchers requiring a hash which I hated having to manually update & like the UX flakes provides (I really wish they supported more than Git & Mercurial tho). You can still have different evals tho if you point to latest.tar.zstd or other non-hashed thing like a branch where the referred to can change & it won’t reproduce. I haven’t used channels in years, but doesn’t that just refer to the running system, not using Nix to build projects?