PokéChamp: an Expert-level Minimax Language Agent
Authors: name: Seth Karten, name: Andy Luu Nguyen, name: Chi Jin

We introduce Pok\'eChamp, a minimax agent powered by Large Language Models
(LLMs) for Pok\'emon battles. Built on a general framework for two-player
competitive games, Pok\'eChamp leverages the generalist capabilities of LLMs to
enhance minimax tree search. Specifically, LLMs replace three key modules: (1)
player action sampling, (2) opponent modeling, and (3) value function
estimation, enabling the agent to effectively utilize gameplay history and
human knowledge to reduce the search space and address partial observability.
Notably, our framework requires no additional LLM training. We evaluate
Pok\'eChamp in the popular Gen 9 OU format. When powered by GPT-4o, it achieves
a win rate of 76% against the best existing LLM-based bot and 84% against the
strongest rule-based bot, demonstrating its superior performance. Even with an
open-source 8-billion-parameter Llama 3.1 model, Pok\'eChamp consistently
outperforms the previous best LLM-based bot, Pok\'ellmon powered by GPT-4o,
with a 64% win rate. Pok\'eChamp attains a projected Elo of 1300-1500 on the
Pok\'emon Showdown online ladder, placing it among the top 30%-10% of human
players. In addition, this work compiles the largest real-player Pok\'emon
battle dataset, featuring over 3 million games, including more than 500k
high-Elo matches. Based on this dataset, we establish a series of battle
benchmarks and puzzles to evaluate specific battling skills. We further provide
key updates to the local game engine. We hope this work fosters further
research that leverage Pok\'emon battle as benchmark to integrate LLM
technologies with game-theoretic algorithms addressing general multiagent
problems. Videos, code, and dataset available at
https://sites.google.com/view/pokechamp-llm.