Willison urges default hard budget caps for pay-by-usage APIs
Simon Willison argues that pay-by-usage services and APIs need default hard budget caps, not soft warnings, to prevent runaway costs from coding and personal agents. He warns that soft caps, which only send warning emails, are insufficient because agents can consume hundreds or thousands of dollars overnight while users sleep.
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Simon Willison
Here's a product feature which the world is going to need a whole lot more of over the coming months and years: default hard budget caps . I'm talking about the feature of pay-by-usage services and APIs that lets you say "after $X/month, cut this thing off and return errors". These need to be hard limits. Soft caps, "after $X/month, send me a warning email", will not cut it. Coding agents, and personal agents (coding agents wrapped in a less threatening UI), greatly reduce the friction of spinning up code that can do useful things. Sometimes those things cost money - calls to paid APIs, or hosted web applications, or systems that can bill for additional storage and compute. Nobody wants to wake up to an email sent at midnight warning about a budget limit and find that, while they slept, their rogue service had consumed several hundred (or several thousand) more dollars of usage. An argument against this is that businesses don't want their hosted applications to start throwing errors be