SkillGym is a framework that turns human-written , which are normally used as external instructions, into executable training environments. It does this by instantiating concrete tasks from skill descriptions, verifying outcomes with code-based checkers, and identifying tasks that truly require the skill through contrastive runs.
The authors released 2,756 environments across 12 categories and collected 8,364 successful trajectories. Fine-tuning a 35B model on this data improved its performance on general agent benchmarks (e.g., +199 Elo on GDPval-AA v2) and on skills benchmarks, allowing it to surpass the reported scores of much larger models like Claude Sonnet 4.6 and GPT-5.4 Mini.