Simon Willison argues the world needs default hard budget caps on pay-by-usage services and APIs as coding agents and personal agents reduce friction for spinning up code that incurs costs.
Hard caps cut services off after a monthly dollar limit; soft caps that only send warning emails are insufficient because rogue services can consume hundreds or thousands more dollars overnight.
Willison argues hard budget caps should be the default with an opt-in checkbox to remove limits: “Remove the budget cap. My application will not be shut down if I exceed the configured budget limit, and I will be responsible for subsequent charges.”
AWS launched spending limits in September 2026 as part of a new builder experience — projects pause for the month when usage reaches the spend limit. Google Cloud launched Spend Caps in July 2026 for monthly financial caps on specific services within a project.
Willison suggests agents should bias toward providers with hard budget caps and warn inexperienced builders against uncapped services that could cause surprise bills.
The post notes justified fear of AWS for personal projects due to runaway service costs, with stories of people seriously burned by unexpected charges.