Anubis is based on hashcash concepts - just adapted to a web request flow. Basically the same thing - moderately expensive for the sender/requester to compute, insanely cheap for the server/recipient to verify.

We need bitcoin-based lightning nano-payments for such things. Like visiting the website will cost $0.0001 cent, the lightning invoice is embedded in the header and paid for after single-click confirmation or if threshold is under a pre-configured value. Only way to deal with AI crawlers and future AI scams.

With the current approach we just waste the energy, if you use bitcoin already mined (=energy previously wasted) it becomes sustainable.