Arena AI is a crowdsourced platform where users submit prompts to two anonymous AI models simultaneously, vote on the better response, and collectively shape a public Elo-based leaderboard. Originally launched in 2023 as Chatbot Arena by UC Berkeley researchers, it has grown to cover 360+ models across categories including text, coding, math, creative writing, and image generation. The platform is free to use, with no account required for basic access, and an enterprise AI Evaluations tier is available for structured commercial testing. As of early 2026, Arena AI serves over 5 million monthly active users across 150 countries.