> ## Documentation Index
> Fetch the complete documentation index at: https://docs.nozle.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Consumable Metrics

> Model usage behavior independently from aggregation lifecycle

Every new Feature explicitly chooses two independent concepts.

## Usage behavior

* **Consumable:** each measured unit may spend an allowance or credit balance.
* **Continuous:** represents a current allocation such as seats or storage.

## Aggregation lifecycle

* **Periodic (`recurring=false`):** the aggregate starts over for the next billing period.
* **Persistent (`recurring=true`):** The billing engine carries the calculated metric state across periods.

`consumable` is never inferred from `recurring`. A lifetime token pool can be consumable and persistent; a seat count is continuous and normally persistent.

Only metrics with `consumable=true` can join a Phase 1 Credit System. Existing metrics with `consumable=null` continue ordinary usage pricing and invoicing, but cannot spend product credits until classified.

Phase 1 credit deduction supports deterministic per-event deltas:

* `count_agg`: one event equals one metric unit;
* `sum_agg`: units come from the configured numeric field.

Stateful or whole-period aggregations remain available for normal usage billing but are not eligible for credit mappings yet.