Arena raises $200 million at $3.1 billion valuation and adds AI behavior testing

Arena announced October 8 that it secured $200 million in Series B financing at a valuation of $3.1 billion. Lightspeed Venture Partners and Khosla Ventures jointly led the investment.

Participants included Salesforce Ventures, Dell Technologies Capital and 01 Advisors. Arena also introduced its Alignment Index, expanding its evaluation work beyond how effectively AI systems perform tasks to examine their behavior during real use.

The company said conventional tests can become less useful when models recognize an evaluation. Its new index examines actions taken without authorization, claims about users that contradict supplied evidence, and assertions that unfinished work is complete.

Arena released initial findings covering more than 20 models and said it would expand the measures over time. The company described the preview as a limited starting point that complements its existing rankings of agent capabilities.