Pricing and usage

Calculate from actual usage and the rate valid at request start. Persist the applied snapshot; do not reprice old calls with today's catalog.

Example

// 示例：供已有 catalog 配置的调用方计算当次费用；无价格时显式处理失败。
charge, priced := catalog.CostAt("company-chat", catalog.Usage{
    PromptTokens: 1500, CompletionTokens: 100,
}, startedAt)
if !priced {
    return fmt.Errorf("model has no applicable price")
}
_ = charge.Total

Contract

The fragment runs inside a function importing fmt and internal/catalog; startedAt is a time.Time and company-chat must have configured rates.

Measure	Rule
Normalized rate	quantity × usd; do not divide by unit_size again
Cache reads	Subset of input tokens, not additional input
Media	Actual successful output, not requested duration
Historical logs	Read price_snapshot
Queue	Commit PostgreSQL before Redis Ack

There is no budget reservation or separate provider-cost/customer-price ledger. Response cost headers are not a durable commit receipt. Failed/missing billing evidence is not proof of free usage.

Source and verification

internal/catalog/cost_at.go

go test ./internal/catalog ./internal/iam ./internal/live -count=1

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