Arena, the crowdsourced AI model ranking platform that began as a 2023 UC Berkeley research project, has raised 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 also participating. The company previously announced a $150 million Series A in January at a $1.7 billion post-money valuation, when its annualized revenue was $30 million. It said it reached $100 million in annualized run-rate revenue in June, putting its valuation nearly double in about 10 months.

Arena‘s platform is free for consumers, who enter prompts or request vibe-coded projects and then rate which model does it better. The company says it draws tens of millions of monthly visitors. In September of last year, it introduced its commercial product, AI Evaluations, which provides model labs and enterprises with detailed performance analytics built from community feedback.

The timing proved important: this year, AI labs recognized that models were gaming benchmarking tests, finding ways to score well without truly earning the results. Enterprises also wanted help picking the model that works best for their own internal needs rather than relying only on standardized benchmarks. Arena‘s funding announcement argues that static benchmarks break down once models recognize they are being tested, and that the world needs a neutral third party to measure how safe and aligned AI actually is once it is in the hands of real people.

To that end, Arena added a new alignment category to its leaderboard, ranking models on issues such as unauthorized action, false attribution, and what it calls deceptive completion. Its preliminary alignment leaderboard currently has a slate of OpenAI models at the top, with Claude Opus 5.5 and Claude Fable in sixth and ninth place, respectively.