Code World Models for General Game Playing

Researchers at Google DeepMind introduced Code World Models (CWM), a framework that uses Large Language Models to translate natural language game rules and player trajectories into executable Python code. Unlike traditional methods that use LLMs as direct move-generating policies, this approach treats the model as a verifiable simulation engine capable of defining state transitions and legal actions. The generated code serves as a foundation for high-performance planning algorithms like Monte Carlo tree search (MCTS), which provides significantly greater strategic depth. The framework also synthesizes inference functions to estimate hidden states in imperfect information games and heuristic value functions to optimize search efficiency. Evaluated across ten diverse games, the CWM agent consistently matched or outperformed Gemini 2.5 Pro, demonstrating superior generalization on novel, out-of-distribution games. This shift from "intuitive" play to System 2 deliberation allows the agent to maintain formal rule adherence while scaling performance with increased computational power.