GEM is a Gym-like framework for training and evaluating agentic LLMs via reinforcement learning. It provides a diverse set of environments (games, math, code, QA, etc.) that can be used to train LLMs to interact with tools, solve problems, and make sequential decisions. The framework features a modular design with composable wrappers for observation modification, tool integration, and episode tracking, along with vectorized environments for parallel execution. It supports integration with multiple RL training frameworks (Oat, Verl, Tinker, OpenRLHF, RL2) through example scripts, making it a versatile tool for LLM agent research.