companies

LMArena

Runs the blind, crowdsourced voting site (formerly LMSYS Chatbot Arena) that ranks frontier AI models by human preference instead of static benchmark scores.

LMArena grew out of a UC Berkeley research project started in 2023 by researchers including Ion Stoica, who wanted a way to compare chatbots that didn't rely on static academic benchmarks. Under the LMSYS name, they built Chatbot Arena: a user submits a prompt, two anonymized models answer side by side, and the voter picks a winner. Those votes are aggregated into a Bradley-Terry ranking that has become a widely cited reference point for how models actually compare in use. The project spun out into an independent company, LMArena, in April 2025 and quickly attracted institutional backing: a $100 million seed round led by Andreessen Horowitz and UC Investments in May 2025, followed by a $150 million Series A in January 2026 at a roughly $1.7 billion valuation. Co-founders Anastasios Angelopoulos and Wei-Lin Chiang serve as CEO and CTO, with Stoica staying on as chairman. By mid-2026 the platform had logged millions of head-to-head votes across hundreds of models, spanning dedicated arenas for text, coding, vision, and other categories, and AI labs routinely cite their Arena rank alongside internal benchmarks when announcing new models.

Founded

2025

Headquarters

San Francisco, United States

Sector

data