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The Agent OS for enterprise customer experience, led by Bret Taylor
HQ: San Francisco, CA | Founded: 2023 | Employees: ~300-500 (2026 press range) | Stage: Private; $15.8B valuation (May 2026) | Website: https://sierra.ai
Sierra AI, founded February 2023 in San Francisco by Bret Taylor and Clay Bavor (who met at Google), publicly launched in February 2024 with an $110M seed at ~$1B valuation. Its Agent OS 2.0 runs AI agents across voice, chat, SMS, email, and physical stores, routing across a constellation of 15+ models (OpenAI, Anthropic, Meta, Google) with deterministic brand guardrails. The company raised $175M at $4.5B (Oct 2024), $350M at $10B (Sep 2025), and a $950M Series E at $15.8B (May 2026, Tiger Global + GV), plus a SoftBank Vision Fund 2 investment tied to Japan expansion and the Opera Tech acquisition (Mar 2026). ARR reached $200M in nine quarters. Customers include Prudential, Cigna, BCBS, SoFi, Rocket Mortgage, Nordstrom, Wayfair, Ramp, Rivian, Sonos, ADT, SiriusXM, Nubank, Singtel, and NEXT
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