Learning to summarize from human feedback
Nisan StiennonLong OuyangJeff WuDaniel M. ZieglerRyan J. LoweChelsea VossAlec RadfordDario AmodeiPaul Christiano
Demonstrates that fine-tuning language models with reinforcement learning on human preference comparisons produces summaries preferred by human evaluators over those generated by standard supervised learning or human reference authors.
The paper describes a method for training language models to produce higher-quality summaries by directly optimizing for human preferences rather than using proxy metrics. Current approaches to summarization rely on supervised fine-tuning to match human-written reference summaries and automatic evaluation with metrics such as ROUGE. These proxies often diverge from what people actually judge as good summaries, leading to factual errors, poor coverage, and other problems that are hard to fix with maximum-likelihood training alone.
The work set out to close that gap by collecting human judgments of summary quality, learning a model that predicts those judgments, and then using the resulting model as a reward signal for reinforcement learning. Researchers gathered more than 64,000 pairwise comparisons of summaries on a filtered version of the Reddit TL;DR dataset. They trained reward models ranging from 1.3 billion to 6.7 billion parameters to predict which summary a human would prefer. They then fine-tuned GPT-style policy models with proximal policy optimization, adding a KL penalty to keep outputs close to the supervised baseline. The process was repeated in batches, and the same reward models were later used to evaluate transfer to the CNN/Daily Mail news domain without further fine-tuning.
Human feedback policies produced summaries that labelers preferred to both the original reference summaries and to much larger models trained only with supervised learning. A 1.3 billion parameter feedback model outperformed a 10-times-larger supervised model, and the 6.7 billion parameter feedback model was rated highest overall. On CNN/Daily Mail the same Reddit-trained feedback models generated fluent, high-coverage summaries that nearly matched the quality of models fine-tuned directly on news data. The learned reward models agreed with human raters at rates comparable to inter-rater agreement and outperformed ROUGE at predicting preferences. Scaling both model size and the amount of comparison data improved reward-model accuracy, while excessive optimization against a fixed reward model eventually produced worse summaries.
These results show that reward modeling from human feedback can measurably improve output quality on a subjective generation task and can generalize across domains. The approach offers a practical route to aligning model behavior with nuanced human criteria that are difficult to capture in hand-crafted loss functions. It also demonstrates that such alignment remains feasible at the scale of current large language models.
Further work is needed to reduce the cost of data collection, to test whether similar gains appear on longer or more open-ended tasks, and to develop safeguards against reward hacking. The released dataset of comparisons and the inference code for the 1.3 billion parameter models provide a starting point for that research. The main limitations are the expense of high-quality human labels and the risk that over-optimization against an imperfect reward model can degrade performance once a certain threshold is crossed.
- Paper: Deep reinforcement learning from human preferences, Paul F. Christiano et al. (2017). Reading Christiano et al. (2017) first is essential because it introduces the foundational framework of training deep reinforcement learning agents directly from human preference comparisons rather than fixed programmatic rewards.
- Paper: Fine-Tuning Language Models from Human Preferences, Daniel M. Ziegler et al. (2019). Ziegler et al. (2019) directly precedes this paper by first demonstrating how to apply reinforcement learning from human preferences to fine-tune language models for summarization.
- Paper: ROUGE: A Package for Automatic Evaluation of Summaries, Chin-Yew Lin (2004). Familiarity with the ROUGE evaluation package is required to understand the metric limitations that motivated shifting from automatic proxies to human preference optimization.
- Paper: Direct Preference Optimization: Your Language Model is Secretly a Reward Model, Rafael Rafailov et al. (2023). Rafailov et al. (2023) directly extends this work by introducing Direct Preference Optimization (DPO), which eliminates the separate reward modeling and reinforcement learning steps used in the source paper.
- Paper: Scaling Laws for Reward Model Overoptimization, Leo Gao et al. (2023). Gao, Schulman, and Hilton (2023) naturally continue this research by studying the reward model overoptimization and scaling laws that occur when fine-tuning policies against human-preference reward functions.
- Paper: From Generation to Judgment: Opportunities and Challenges of LLM-as-a-judge, Dawei Li et al. (2025). This survey paper builds upon the human feedback paradigm established in the source by exploring broader opportunities and challenges of using large language models as judges.
