Sierra

Customer-service AI agents, Agent OS

US$15B privateest. 2023sierra.ai (opens sierra.ai)Checked 11 Oct

The brief

Analyst view
  • Passed $150M in annual recurring revenue in February 2026, two years after its public launch.
  • Raised $950M in May 2026 at a valuation above $15B, led by Tiger Global and GV.
  • Customers include SiriusXM, ADT, Cigna, Rocket Mortgage, Nordstrom and Rivian; more than 40% of the Fortune 50.

Technical approach

As reported
Models

Many models behind one agent

Agents draw on more than 15 open and proprietary models rather than depending on a single lab.

Building

From code to plain-English specs

Developers use the Agent SDK, business teams Agent Studio; Ghostwriter builds an agent from a written procedure or call transcripts.

Pricing

Paid per outcome

Customers pay when an agent actually resolves an issue or completes a business goal, not per message or per token.

Testing

Simulated customers

Its tau-bench benchmark has AI play a customer against the agent many times, measuring whether it follows policy consistently, not just once.

Primer