Sierra

Sierra is a conversational AI platform that helps enterprises build, deploy, and manage AI agents for customer service. Founded by Bret Taylor and Clay Bavor, Sierra's agents handle customer interactions across chat and voice — from answering questions to taking actions like processing returns and updating subscriptions. In May 2026 Sierra raised $950M at a valuation above $15B, led by Tiger Global and GV, following a $350M round at a $10B valuation in September 2025.