Billing by the minute needs a ledger of every conversation, which means your deployment has to report what it did to somebody else's server. That single requirement is what makes a metered vendor hard to approve in a regulated setting, and it is the thing this product exists to avoid.
So the meters are things readable from your own database at a single instant: conversations running at once, agents configured, admin seats, documents indexed. No history, nothing to report, nothing to audit.
We hold no certification on your behalf. Self-hosting means the compliance posture is yours, which is the point for most buyers who ask.