reinforcement learning from human feedback (RLHF)

Reinforcement learning from human feedback (RLHF) is a training technique that aligns a large language model with human preferences by using human comparisons of model outputs to shape the model’s behavior.

A typical RLHF pipeline runs in three stages:

• Supervised fine-tuning on human-written prompts and responses to give the base model instruction-following behavior.
• Reward model training, where annotators rank pairs of model outputs and a separate model learns to predict those preferences as a scalar reward.
• Policy optimization with a reinforcement learning algorithm, typically proximal policy optimization (PPO), that maximizes the reward while a Kullback-Leibler divergence penalty discourages drift from the supervised baseline.

RLHF was popularized by InstructGPT and is used to align assistants such as ChatGPT, Claude, and Gemini. Related methods include direct preference optimization (DPO), a direct alignment algorithm that optimizes the same preference objective with a supervised loss and needs no separate reward model or reinforcement learning loop, and reinforcement learning from AI feedback (RLAIF), which replaces human annotators with another model. A third approach, reinforcement learning from verifiable rewards (RLVR), swaps the learned reward model for automatic checkers such as unit tests or math graders, and it has become the dominant post-training method for reasoning models, usually paired with group relative policy optimization (GRPO) rather than PPO. Known limitations include reward hacking, sensitivity to annotator agreement, and bias inherited from the preference data.

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