Arena has raised a $200M Series B at a $3.1B valuation, nearly double the $1.7B post-money figure from its January Series A.
The round was led by Lightspeed Venture Partners and Khosla Ventures, with Salesforce Ventures, 01 Advisors, Dell Technologies Capital, Endeavor Catalyst, a16z, Felicis and others participating.
Arena began in 2023 as a UC Berkeley research project that crowdsourced rankings of AI models. Consumers use it free, entering prompts or requesting small vibe-coded projects and then rating which model did better. The company says it sees tens of millions of monthly visitors.
Its commercial turn came in September 2025 with AI Evaluations, a paid service that gives labs and enterprises performance analytics drawn from that community feedback. The timing was lucky. As models learned to game static benchmarks, buyers started asking for evidence closer to their own workloads. Arena said it hit $100M in annualized revenue in June, up from $30M at the start of the year.
The bet is that evaluation becomes a durable business as model quality converges and the differentiator shifts to knowing which one is right for a given job.
