A surrogate unit is the abstracted unit a vendor uses to invoice across heterogeneous actions — e.g., one credit pool consumed at different rates by conversation resolutions, prospecting recommendations, data prompts, dataset queries, and intent-monitoring months. The buyer pays in one unit; the vendor reconciles against many. The conversion table between the surrogate unit and the underlying value metrics is the vendor's margin lever — it can be re-rated at renewal, accelerated for specific feature classes, or expanded with new action types without changing the headline unit price. Surrogate units typically coexist with non-surrogate passthrough charges (telephony minutes, SMS, raw API costs) that the meter does not capture, fragmenting the bill across the surrogate layer and a parallel passthrough layer. A credit is a minted currency, which is why it is a surrogate licensing unit rather than a metric family: a conversion layer laid over products a customer was licensed for on different bases across its history, with the rate card underneath defining the exchange rate.