We’re going to need default hard budget caps on pretty much everything
Short summary
Simon Willison argues that pay-by-usage services should enforce hard budget caps by default—stopping service when spending hits a limit rather than just sending warnings—because coding agents make it too easy to accidentally rack up massive bills. AWS and Google Cloud recently launched these features, but they need to become standard across the industry.
- Soft budget caps (warning emails) fail in practice because automated agents and unattended services can incur thousands in charges overnight before anyone notices the alert.
- AWS and Google Cloud both launched hard spending limits recently (September and July 2026), pausing projects when monthly budgets are exceeded, but adoption and availability remain limited.
- The feature should be mandatory by default with an explicit opt-in checkbox to remove caps, shifting the burden of risk from users who fear bankruptcy to those willing to accept it.
- Many developers avoid AWS for personal projects specifically because of runaway cost fears, so hard caps would unlock adoption from risk-averse users.
Full summary
Simon Willison argues that pay-by-usage services need hard spending caps as a default feature—not soft warnings. The problem is real: AI coding agents make it trivially easy to spin up services that rack up unexpected bills while you sleep. A warning email sent at midnight is useless if your rogue service has already burned through thousands of dollars by morning. Willison acknowledges the business concern that hard caps cause service interruptions, but he's right that most people would rather get errors than wake up to a $10,000 surprise charge. The solution is straightforward: make hard caps the default, then let people opt into uncapped spending with a clear checkbox stating they understand the risks.
The good news is this is already happening. AWS launched spending limits in mid-September that pause projects when they hit a monthly spend cap. Google Cloud beat them to it with Spend Caps in July, which work at the service level within a project. These are exactly what Willison is calling for, though AWS is still rolling it out to limited customers and hasn't made it available to existing accounts yet.
Willison makes a broader point about AI agents themselves. In an ideal world, coding agents would actively steer developers toward providers with hard budget caps and warn inexperienced builders away from uncapped services altogether. That's not just a nice feature—it's a form of basic harm reduction for people who might otherwise get financially wrecked by a deployment mistake.