Arena, the A.I. Leaderboard, Is Now Worth $3.1 Billion

Arena, the company better known until recently as Chatbot Arena and LMArena, has locked in a $200 million Series B at a $3.1 billion valuation. Lightspeed Venture Partners and Khosla Ventures led the round, with Salesforce Ventures, 01 Advisors, Dell Technologies Capital, Endeavor Catalyst, a16z and Felicis all in the mix.

That’s a sharp jump from January, when Arena raised $150 million at a $1.7 billion valuation. The company also says its annualized revenue climbed from $30 million then to $100 million by June. Most of that money comes from AI Evaluations, a paid product that gives labs and companies analytics built from community ratings.

Arena started in 2023 as a research project at the University of California, Berkeley. The setup is simple and a little brutal: users ask a question, two anonymous models answer, and people vote on which response is better. Multiply that by millions of duels and you get a leaderboard that Arena says attracts tens of millions of visitors each month.

Now it is trying to turn that same machinery toward AI agents. The new alignment index is based on about 90,000 real sessions and tracks problems like agents taking actions without permission, misattributing sources, or claiming they finished tasks they never actually completed. In the preliminary ranking, OpenAI models are out front, with GPT-6.1 Sol in first place at 87.9 points, while Anthropic’s Claude Opus 5.5 is sixth.

That matters because these rankings are more than nerd candy. They are a sales pitch. New models such as Mistral Large 4 are routinely launched with their Arena placement in the headline, and the scores feed directly into the price fight between OpenAI and Anthropic. Arena says static benchmarks stop working once models know they are being tested, which is a fair point — and also a very convenient one for a company sitting on the scoreboard.