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LLM call cost estimation fails, post-call reconciliation is key

Estimating the cost of Large Language Model (LLM) calls before they are made is proving to be an unreliable method for implementing spending caps. A recent experiment with OpenRouter and the `openai/gpt-oss-20b:free` model revealed that pre-call estimates were highly inaccurate, often underestimating costs by significant margins, especially for calls without a specified `max_tokens`. This inaccuracy means that tightening caps to prevent overspending would also block legitimate calls, while loosening them to allow valid usage would permit the very unbounded, expensive calls the caps are meant to prevent. The most effective approach appears to be reconciling costs after each call and stopping when a cumulative cap is reached, accepting a potential single-call overshoot as a trade-off for functional budget management. AI

IMPACT Highlights a critical operational challenge for AI developers and businesses in managing LLM expenses, suggesting a more reliable reconciliation-based approach.

RANK_REASON Article discusses the practical challenges and limitations of cost estimation for LLM API calls, offering an opinion on alternative solutions.

Read on dev.to — LLM tag →

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LLM call cost estimation fails, post-call reconciliation is key

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  1. dev.to — LLM tag TIER_1 English(EN) · focxle ·

    You cannot predict what an LLM call will cost before you make it

    <p>I spent a week building spending caps for AI agents on an assumption that turned out to be wrong, and the way it was wrong is more interesting than the feature.</p> <p>The assumption is the obvious one. Before making a model call, estimate what it will cost. If that estimate b…