Sierra builds an enterprise AI agent platform that lets companies replace or augment call centers and digital support with autonomous AI agents. Enterprises configure agents through Sierra's Agent OS — a layer sitting on top of 15+ frontier and open-weight models — then deploy them across chat and voice channels to handle customer service, insurance claims, mortgage origination, subscription management, and more. Customers pay per conversation or per successful resolution, not per seat. The platform includes tooling to build, test, monitor, and continuously improve agents without writing model code. Named clients include Uber, Rivian, CLEAR, SiriusXM, and Sutter Health, skewing heavily toward Fortune 50 enterprises. Founded in 2023 by Bret Taylor (former Salesforce Co-CEO, OpenAI Chairman) and Clay Bavor (former Google Labs head), Sierra is now present in 10+ cities across North America, Europe, and Asia-Pacific.