When developers worry about runaway AI API costs, they think about infinite loops. An agent that retries indefinitely. A bug that sends the same request ten thousand times. Something obviously broken.

That's the #1 cause. It's dramatic, it's usually caught quickly, and it's fixable with a simple retry limit.

The #2 cause is quieter and more expensive over time: verbose prompting .

Here's the math. An orchestrator writes a prompt to dispatch a subagent. It explains the objective, provides context, restates constraints, includes examples, describes what was already tried. The prompt is 2,000 tokens. The subagent runs for 1,500 tokens of output. One call: 3,500 tokens.

Now the orchestrator dispatches 6 subagents, each with a similarly verbose prompt. The operation is 21,000 tokens. The orchestrator runs this twice a day.…