Named seat includes admins, supervisors, agents, and developers (e.g. any TaskRouter worker). Twilio charges customers for the maximum number of named users that were on the account for a given month.
We do not prorate the addition or deletion of named seats mid-month, with one exception. When a customer transitions from a starter Flex project to the named seat model, we will prorate named seats at that time to prevent double billing.
Example: If a customer starts the month with 50 users, removes 25 of them mid-month, and then adds another 25 to replace them, they would be charged for 50 total named users that month. We will not double bill for the additional seats they added.