# Usage and spend

How model usage is metered per run, where you read it, and how a session budget bounds what an agent can spend.

Every model call goes through the tenant's LLM gateway, which meters it against the run that made
it. Usage therefore rolls up from runs to sessions, agents, and the principals who started them,
and a session can carry a budget that bounds it.

> **Availability:** Metering and budgets are enabled per tenant; a session shows usage as not measured where they are off. See [What is available where](/reference/availability).

- Usage is recorded per run: input tokens, output tokens, and the model.
- The Console's session view shows usage by run and, where a budget governs the session, the
  cap, what is reserved, what has settled, and what remains.
- A run that would exceed the session's budget is refused before it starts, not cut off midway.

## Read usage

Open a session in the Console and choose the tokens panel. It shows totals for the session and a
breakdown by run, split into input and output. The same numbers are attributed in the execution
trace's model-call spans, so an evaluation experiment can report cost beside quality.

## Budgets

Where a session budget is set, the panel shows:

| Figure | Meaning |
|---|---|
| Cap | The session's budget |
| Reserved | Usage held for a run that is still executing |
| Settled | Usage recorded for completed runs |
| Available | Cap minus reserved minus settled |

A run is admitted only if its reservation fits. "No budget governs this session" means the
session has no cap, and usage is metered but unbounded.

## Where spend is decided

Spend is a consequence of three declarations you already control: the models in
`permitted_models`, the tools the agent may call, and how long sessions live. A cheaper model in
the allowlist that your application selects for routine requests is the largest lever. See
[Choose models](/guides/build/choose-models).

## Where to go next

- [Sessions and runs](/concepts/sessions-and-runs)
- [Evaluate a version](/guides/evaluate/evaluate-a-version): cost beside quality for a
  candidate.