A Practical Guide to LLM Cost Accounting and Token Metering

LLM cost accounting looks simple from far away: multiply tokens by price. In production, it becomes more subtle. Input and output tokens have different prices. Providers expose usage in different shapes. Streaming responses may report usage at the end. Some providers may omit usage for certain failures.

Separate response speed from accounting finality

Do not block the model response on heavy accounting work. The request path should stream as soon as upstream data is available. Usage capture, cost calculation, and credit ledger writes should happen as the response completes, not as a precondition for letting the response begin.

Keep pricing in one catalog

If pricing is copied into multiple places, it will drift. A gateway should have one canonical model catalog with provider, slug, display name, context window, capability flags, input price, output price, and enabled status. The router, dashboard, and database seed should all use that same source of truth.

Record request-level facts

A credit balance is not enough. Teams need request records: model slug, provider, status, input tokens, output tokens, cost, latency, time to first byte, error code, source API key, and timestamp. Without that detail, spend becomes impossible to explain.

Avoid fake precision and wasteful rounding

Rounding every request up to one cent makes cheap models look more expensive than they are. Sylica stores credits with fractional precision so low-cost requests can debit true metered cost while the dashboard still formats amounts for humans.