Enterprise AI for autonomous customer service agents. Sierra is an enterprise AI startup headquartered in San Francisco, California. The company was founded by Bret Taylor and Clay Bavor, leaders in the tech industry, and specializes in building autonomous AI agents for complex customer service workflows using their proprietary Agent OS platform. Sierra’s platform ensures accuracy and brand consistency, automates tasks such as refunds, scheduling, and policy updates, and supports multilingual interactions. The company has rapidly gained high-profile enterprise clients, including WeightWatchers, Sonos, SiriusXM, SoFi, Brex, and Ramp. Working with a team of approximately 150 employees, Sierra has seen impressive financial growth—raising a $175M funding round at a $4.5B valuation in late 2024, and securing an additional $350M in 2025 at a $10B valuation.