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. In a week, that's 294,000 tokens — at Sonnet rates, about $1.35 in input costs alone.…