Simon Willison · 2026-10-03 · notable
Simon Willison — usage-billed services need hard budget caps by default
Simon Willison argues that pay-per-use services should stop spending at a hard cap by default, with uncapped billing as an opt-in. Coding agents make it easy to spin up code that can run up a surprise bill.
A warning email is not a limit: services should pause at your budget unless you opt out.
What is it?
Simon Willison's post calls default hard budget caps a feature the world will need a lot more of. A soft cap only sends a warning, which does not stop charges piling up while you sleep. A hard cap pauses the service when spending reaches the limit, and Willison wants that to be the default, with uncapped billing behind an explicit checkbox.
How does it work?
Willison points to two providers that now offer the real thing. AWS launched spending limits in September 2026: you set a monthly limit for a project, and if usage reaches it the project is paused for that month. Google Cloud added Spend Caps in July, which put a monthly financial cap on specific services in a project.
Why does it matter?
Coding agents, and personal agents built on them, remove most of the friction from spinning up code that does useful things, and that code can also run up bills. Willison suggests agents could help by preferring providers that offer hard caps when they recommend where to deploy. For anyone who avoids usage-billed clouds for side projects out of fear of a five-figure surprise, the post explains what to look for.
Who is it for?
developers deploying side projects and agent-built apps