Arena raises $200M Series B at $3.1B valuation to expand AI model evaluation platform

Arena, which began as a 2023 UC Berkeley research project crowdsourcing AI model rankings, raised a $200 million Series B at a $3.1 billion valuation, the company said. 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 previously raised a $150 million Series A in January at a $1.7 billion post-money valuation, when it reported $30 million in annualized revenue. By June 2026, the company said revenue reached $100 million in annualized run-rate.

Arena operates a free crowdsourced platform where users rate model responses to prompts and projects. The company claims tens of millions of monthly visitors. In September 2025, Arena launched AI Evaluations, a paid service providing performance analytics to model labs and enterprises based on community feedback.

The timing coincided with growing concerns that models were optimizing for static benchmarks rather than real-world performance. Arena argues that "AI is advancing faster than our ability to evaluate it, and static benchmarks break down once models recognize they’re being tested."

To address alignment and safety, Arena introduced an alignment category on its leaderboard ranking models on issues such as unauthorized actions, false attribution, and what it calls "deceptive completion." As of the announcement, OpenAI models led the preliminary alignment leaderboard, with Anthropic’s Claude Opus 5.5 and Claude Fable ranked sixth and ninth, respectively.