Sierra unveils Curie and Fleming models and a Horizon agent platform at Summit 2026

Sierra announced two new models at Sierra Summit 2026: Curie, which runs the core conversation loop, and Fleming, which detects when a caller is another agent. The company also introduced Tandem Voice, Persona Studio, a reimagined Ghostwriter, and Horizon for long-horizon agent goals, and listed Sierra in the Stripe App Marketplace.