LLM fine-tuning with GRPO

Supervised fine-tuning teaches a model to imitate examples. Reinforcement fine-tuning teaches it to optimize an objective you define, which is how recent open models picked up reasoning, reliable tool use, and consistent output formats. GRPO (Group Relative Policy Optimization) is the method behind a lot of that work, and it is simpler and cheaper to run than the PPO setups that came before it.