Learning to play Diplomacy is a big deal for several reasons. Not only does it involve multiple players, who make moves at the same time, but each turn is preceded by a brief negotiation in which players chat in pairs in an attempt to form alliances or gang up on rivals. After this round of negotiation, players then decide what pieces to move--and whether to honor or renege on a deal. At each point in the game, Cicero models how the other players are likely to act based on the state of the board and its previous conversations with them. It then figures out how players can work together for mutual benefit and generates messages designed to achieve those aims. To build Cicero, Meta marries two different types of AI: a reinforcement learning model that figures out what moves to make, and a large language model that negotiates with other players.