Arena, the LMArena leaderboard company, raises $200M Series B at $3.1B valuation

Lightspeed Venture Partners and Khosla Ventures led the round, joined by Salesforce Ventures, 01 Advisors, Dell Technologies Capital, Endeavor Catalyst, Andreessen Horowitz and Felicis. The round closed on September 22. Arena disclosed it alongside a new Alignment Index, which scores agents on unauthorized actions, false attribution and deceptive completion across about 90,000 sessions and 27 models. Some outlets cite a $2.88B post-money figure, while TechCrunch reports $3.1B. Arena began in 2023 as a UC Berkeley research project. It raised a $150M Series A in January at $1.7B, when annualized revenue was $30M, and said in June that its paid evaluations business had reached a $100M run-rate. Total funding is now about $450M. For model and agent builders, independent evaluation is becoming a paid layer of the stack, and Arena's rankings already shape how buyers see models. Labs and enterprise buyers are likely to start weighing alignment scores, not only capability leaderboards, when they choose agents.