Changelog

Stay up to date with the latest changes to Synthflow.
May 15, 2026

Outbound number pooling for agents

You can now assign multiple outbound phone numbers to one agent and choose the caller ID for each outbound call. See the Outbound Number Pooling guide.

EndpointChange
GET /assistants/{model_id}Returns attached_phone_numbers with each attached number’s number, sid, and slug.
PUT /assistants/{model_id}/phone_numbersAttaches multiple outbound numbers using phone_numbers or phone_number_slugs.
DELETE /assistants/…/{phone_number_slug}Detaches one outbound number from the agent.
POST /callsAccepts from_phone_number to select the outbound caller ID for that call.