# Temporal pricing without rewriting historical invoices

Canonical: https://stevenmoriasi.com/blog/usage-billing-entitlement-ledger
By [Steven Moriasi](https://www.linkedin.com/in/steven-moriasi/).
Source: https://github.com/steven-moriasi/temporal-usage-billing-ledger
Date: 2026-03-06

## Context

Usage-based products — including ones that meter LLM tokens — go wrong when a price change rewrites invoices that already shipped, or when the UI calculates money.

The [Temporal Usage Billing & Entitlement Ledger](https://github.com/steven-moriasi/temporal-usage-billing-ledger) keeps PostgreSQL authoritative for plans, receipts, ratings, invoices, credits, and ledger entries. Redis may cache an entitlement decision until it expires.

## Decision

Prices are effective-dated with non-overlapping versions. Receipts are append-only, with duplicate, conflict, quarantine, and replay paths. A period will not close while accepted usage is unrated. Final invoices are immutable; late adjustments are forward-only. Ledger postings balance. Entitlement decisions are server-authoritative.

## What I rejected

Updating the price row in place, and letting the client submit an amount. Both rewrite history or invent a charge the ledger never posted.

## Failure scenario

Fifty concurrent deliveries of one receipt identity: one accept, forty-nine duplicates. A later price change creates a new version. Invoices already issued stay as they were; the next period rates under the new effective date.

## Evidence

PostgreSQL ledger, reproducible invoice fixtures, and entitlement checks issued by the service. If an agent “checks remaining credits,” it should call this kind of API.

Inspect: [Repository](https://github.com/steven-moriasi/temporal-usage-billing-ledger) · [Run locally](https://github.com/steven-moriasi/temporal-usage-billing-ledger#readme)

_—by [Steven Moriasi](https://www.linkedin.com/in/steven-moriasi/)_