I recently found out my website has been blocked by AI agents, when I had never asked for it. It seems to be opt-out by default, but in an obscure way. Very frustrating. I think some of these companies (one in particular) are risking burning a lot of goodwill, although I think they have been on that path for a while now.
Are you talking about Cloudflare? The default seems indeed to be to block AI crawlers when you set up a new site with them.