If you mean user-agent-wise, I think real users vary too much to do that. That could also be a user login, maybe, with per-user rate limits. I expect that bot

If you mean user-agent-wise, I think real users vary too much to do that. That could also be a user login, maybe, with per-user rate limits. I expect that bot runners could find a way to break that, but at least it's extra engineering effort on their part, and they may not bother until enough sites force the issue.