Simon Willison: agents mean every pay-per-use service needs default hard budget caps

In a 3 October 2026 post, Simon Willison argues that pay-per-use services and APIs need hard budget caps by default: limits that cut the service off and return errors, not warning emails. His reasoning is that coding agents and personal agents make it easy to spin up code that spends money, and most businesses would rather see errors than a surprise bill of $10,000 or more.

What it means If your agents can call paid APIs or provision cloud resources, check whether those services enforce hard spending limits or only send alerts.