A $1,800 mistake that arrived with a perfect error rate. A batch report generator got wired into an autosave hook, so it fired every thirty seconds per open session. Spend climbed from $620 to $2,480 across 23 days with nothing new shipped. Response codes were clean and latency was normal, because at the request level nothing was wrong. Only cost grouped by feature over time had the shape to reveal it. Moving that call behind the manual export button cut the following month by 61%. So tag every call with the feature name and the tenant id before launch, not after your first surprising invoice. The rest of the controls, in the order I'd add them: https://www.duskolicanin.com/blog/chatgpt-saas-without-breaking-bank-2026 #AI #SaaS #OpenAI #SoftwareEngineering