A concurrent session is one live AI conversation running at the same time as another: speech in, model, speech out — pipeline capacity on the GPU plane, not a carrier line. It is the unit outbound plans are sold in, and reading it as a phone line is the most common mistake a buyer makes on the pricing page.
A call claims one from the moment a person answers until the moment they hang up, and it is claimed by the voice runtime rather than by the dialer, because the capacity is only needed once somebody actually picks up. A dial that rings out, reaches a machine on a campaign with no message elected, or is refused before it ever leaves claims nothing at all.
Each outbound plan’s monthly price includes a set number of them, and additional sessions are sold monthly in any quantity, bought and changed from the billing page rather than negotiated with a salesperson. The included counts and the price of an extra session live on the pricing page and are deliberately not retyped here: a rate copied into a definition is a rate that drifts away from the one you are billed.
Inbound callbacks claim from the same pool. A burst of people ringing you back narrows the headroom your outbound campaigns are pacing against, automatically and with nothing for you to configure.