It should definitely be default for all payed APIs. I think every AI provider have this by default.

I've had an AI coding agent enter a doom loop for hours multiple times now. having a budget limit for my openrouter key is helpful, but it's already spent then.

I've been building a thing you can hook into ai workflows that uses multiple detectors if an agent is starting to loop and will then send a kill command to that chain. I don't have any testers for it though.