The Hidden Costs of LLM APIs Your API bill has more line items than you think. 1. System prompts sent on every request — easy to forget. 2. Retries on rate limits or 5xx errors. 3. Tool definitions counted as input tokens. 4. Streaming — pay for full output even if user disconnects. 5. Long contexts — pricing often scales non linearly above 100K tokens. Instrument before you scale.