Are Regtest origin hashes always the same or not?

I would like to know if there are two nodes, each running a regtest network. Will the genesis block digest be the same across nodes? I’m asking because I noticed in chainparams.cpp that regtest takes parameters whereas mainnet and testnet do not.

If not, how should apps like Block Explorer handle this? They may not know the regtest origin hash in advance and may have to query the entire node based on block height, etc. Is that right?