OpenAI Five, OpenAI's reinforcement learning system, won two back-to-back games against OG, the reigning Dota 2 world champion team, at the OpenAI Five Finals event. It was the first time an AI beat the world champions in an esports game. The result demonstrated that scaled-up self-play reinforcement learning could master a complex team-based game, avenging OpenAI Five's losses at The International the previous year.