Series C · AI & Machine Learning · London, United Kingdom · Founded 2023 · 51–200 employees
Sierra is a conversational AI platform co-founded in 2023 by Bret Taylor (former Salesforce co-CEO, OpenAI board chairman) and Clay Bavor (former head of Google Labs), enabling enterprises to deploy brand-aligned AI agents for customer service across chat, voice, SMS, WhatsApp, and email. The company reached $100M ARR in just seven quarters after launch, making it one of the fastest-growing enterprise software companies on record. Sierra has raised a total of $635M, including a $350M round led by Greenoaks Capital in September 2025 at a $10 billion valuation, with additional backing from ICONIQ, Thrive Capital, Sequoia Capital, and Benchmark. Its client base spans hundreds of major enterprises including ADT, SiriusXM, Sonos, Ramp, SoFi, Wayfair, Cigna, and DIRECTV, with 50% of customers having over $1 billion in revenue. The company operates globally with offices in San Francisco, London, New York, Paris, Madrid, Singapore, Tokyo, Toronto, and Atlanta.