Anubis works to the extent it does because in counter-abuse security by obscurity tends to be the best security of them all. Right now Anubis isn't popular enough for many scrapers to try working around, so they don't. But they will pour resources into working around Turnstile and Recapcha. In this regime, the exact challenge is irrelevant. Anubis would be just as effective if the challenge was running a javascript function to add two numbers instead of a proof of work.
Proof of work is just a uniquely dismal basis for a counter-abuse challenge.
And the data says it stopped working for some sites that actually have a lot of data.
We apologize for a period of extreme slowness today. The army of AI crawlers just leveled up and hit us very badly. [...] It seems like the AI crawlers learned how to solve the Anubis challenges. [...] However, we can confirm that at least Huawei networks now send the challenge responses and they actually do seem to take a few seconds to actually compute the answers. It looks plausible, so we assume that AI crawlers leveled up their computing power to emulate more of real browser behaviour to bypass the diversity of challenges that platform enabled to avoid the bot army.