Usage Metering and Billing APIs

A customer has three features: document summaries, support-answer drafts, and product-description generation.

At the end of the month, they see one total. They cannot tell which feature consumed it, which calls were retried, or whether a failed stream was billed.

A metered API needs more than a monthly total. Provide usage with each result, a collection for reconciliation, an estimate before generation, and clear behavior when the spending limit is reached.

1. Name the Unit Before Naming the Price

"The API charges per call" is not enough when calls differ by thousands of times in size