Libbitcoin for Core people

Yes, and I believe any check that requires total or partial order is skipped if below the milestone block. This is what allows a sync in an hour. So, I think it’s still accurate to say that not looking up input prevouts is where the main speedup is.

Looking at a flamegraph of Bitcoin Core IBD, the majority of time is spent looking up input prevouts. That’s why parallelizing that provides a nice speedup. Skipping it entirely though is not possible since we would not have a utxo set at the end, which is not a constraint that libbitcoin has.