AI evaluation platform Arena raises $200M at $3.1B valuation

On October 8, AI model evaluation platform Arena announced a $200 million Series B round at a $3.1 billion valuation, nearly doubling its valuation in about 10 months. Lightspeed Venture Partners and Khosla Ventures co-led the round, with participation from Salesforce Ventures, 01 Advisors, Dell Technologies Capital, Endeavor Catalyst, a16z, Felicis and others.

Arena began in 2023 as a UC Berkeley research project that crowdsourced rankings of AI models. Its consumer platform is free to use: people enter prompts or request vibe-coded projects and rate which model performs better. The company says it has tens of millions of monthly visitors. It reached $100 million in annualized run-rate revenue in June 2026; in January 2026, Arena raised a $150 million Series A at a $1.7 billion post-money valuation, with annualized revenue of $30 million at the time.

In September 2025, Arena introduced its commercial product, AI Evaluations, which provides model labs and enterprises with detailed performance analytics based on community feedback. The company said AI labs discovered this year that models were gaming benchmark tests, while enterprises wanted help identifying which model works best for their own internal needs. Arena also added an "alignment" leaderboard category, ranking models on issues such as unauthorized action, false attribution and deceptive completion. OpenAI models currently lead its preliminary alignment leaderboard, with Claude Opus 5.5 and Claude Fable in sixth and ninth place respectively.