PettingZoo

PettingZoo is a Python library providing a standardized API for multi-agent reinforcement learning (MARL) environments, analogous to Gymnasium for single-agent RL. It offers a wide variety of reference environments and utilities, supporting both sequential (AEC) and simultaneous (Parallel) action paradigms. Currently at version 1.25.0, the library is actively maintained with frequent updates to ensure compatibility with recent Python and Gymnasium versions.