Sierra

Sierra is a U.S. conversational AI company founded in 2023 by Bret Taylor (former Salesforce co-CEO, OpenAI board chair, Google Maps co-creator) and Clay Bavor (18 years at Google, most recently leading Google Labs, Project Starline and AR/VR). The company publicly launched on February 13, 2024 and is headquartered in San Francisco, with offices in New York, Atlanta, London, Singapore, Tokyo, Paris, Madrid and Toronto.

Its flagship product, Sierra Agent OS, is an enterprise platform for building, optimizing and scaling AI agents across chat, SMS, WhatsApp, email, voice and ChatGPT. In 2025 the company unveiled Agent OS 2.0 along with the Agent Data Platform (agent memory, integrations with Snowflake, Databricks, BigQuery, Redis and AWS) and Agent Studio 2.0. In March 2026 Sierra launched Ghostwriter — an agent that builds other agents from SOPs, transcripts, audio recordings, or plain-English descriptions.

Sierra runs on a "constellation of models" architecture — combining frontier models (OpenAI, Anthropic), open-weight models and proprietary specialist models (e.g. Linnaeus and Darwin for retrieval and reranking), automatically switching providers for performance and continuity. Safety is enforced by supervisor models that wrap LLMs to reduce hallucinations and prevent abuse.

The company pioneered outcome-based pricing — customers pay only for autonomously resolved interactions, not seats or tokens. Sierra serves more than 40% of the Fortune 50, including Rocket Mortgage, SoFi, SiriusXM, Sonos, WeightWatchers, Casper, Ramp, Brex, Discord, ADT, CLEAR, Sutter Health, Nubank, Deliveroo, ASOS, Gap, Wayfair, Sweetgreen, Rivian, Redfin, Safelite, Minted, FINRA and Guild.

Funding: Series A in February 2024 ($110M at a $1B valuation, led by Sequoia and Benchmark), Series B in October 2024 ($175M at $4.5B), and a new $950M round on May 4, 2026 led by Tiger Global and GV at over a $15B valuation, giving Sierra more than $1B on its balance sheet. In November 2025 Sierra hit $100M ARR seven quarters after launch; by February 2026 ARR exceeded $150M.

Compliance: SOC 2, HIPAA, GDPR, PCI DSS Level 1 Service Provider, CCPA, CSA STAR, ISO 27001, ISO 42001, EU AI Act. In April 2026 Sierra launched the industry's first fully PCI-compliant payments capability for AI agents across chat and voice.