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.

The model API returned useful text, but its financial contract is incomplete. When each call can cost money, usage is not only an internal billing table or a page in a portal