--mode, a limit is advisory (continue); pass --mode stop to stop billable work at the limit. --credits none cannot be combined with --mode stop. Each intentional change gets its own retained key; repeat an uncertain request with the original arguments/key.
The limit uses a UTC calendar month. Stop rejects new billable work with project_budget_exceeded and pauses the app when measured usage plus reservations reach the limit: Dev and Prod answer HTTP 402 Project execution paused. Raise or remove the limit, switch to Continue, or wait for the next UTC month; serving resumes within about five minutes. Continue keeps the app and work running after the threshold. Existing work and delayed measurements may settle later, so final costs can exceed the limit.