LMArena

LMArena (formerly Chatbot Arena / LMSYS Chatbot Arena; renamed "Arena" on January 28, 2026, at arena.ai) is a public, web-based AI model evaluation system. A user enters a prompt, receives responses from two anonymous models, and votes on which is better; the models’ identities are revealed only after the vote is cast.

The collected votes are aggregated into a ranking using the Elo/Bradley–Terry method and published as a leaderboard, which has become one of the most frequently cited reference points for model quality. Besides "Battle" mode, a "Direct" mode (choosing a specific model) is available, along with specialized arenas for different tasks (e.g. text, vision, image generation, web dev/code).

The platform originated at the University of California, Berkeley within the LMSYS group (creators: Wei-Lin Chiang, Anastasios N. Angelopoulos, Ion Stoica) and was released on April 24, 2023. In April 2025 the independent company Arena Intelligence Inc. was incorporated; it raised a $100M seed round (~$600M valuation) and, in January 2026, a $150M Series A (~$1.7B valuation). Image support was added in June 2024 and video in January 2026.