Skywork-Reward: Bag of Tricks for Reward Modeling in LLMs
Written for the Research library (claude-opus-5-5) from the paper text, in our own words: the license "arXiv — non-exclusive licence to distribute" does not allow redistributing the text itself. Original — arxiv.org/pdf/2410.18451
Summary
Reward models turn human preferences into a training signal for LLM alignment. Their quality depends heavily on the preference data, and open-source preference datasets tend to be noisy or inconsistently labelled. The authors take a data-first approach. Using only public sources (HelpSteer2, OffsetBias, WildGuardMix and several Magpie subsets), they reduce a pool of about 378K preference pairs to a compact set of about 80K through selection and filtering. They then train discriminative reward models on Gemma-2-27B and Llama-3.1-8B and compare several loss functions. The plain Bradley-Terry objective works best. As of October 2024, Skywork-Reward-Gemma-2-27B ranked first on the RewardBench leaderboard. The team also found that some training prompts overlapped with RewardBench prompts. They released a cleaned v0.2 of the dataset, and retraining on it raised scores slightly. The work shows that a small, carefully chosen dataset can beat much larger collections. The released data has already been used to build other leading reward models.
Key points
- Data: Skywork Reward Preference 80K is built from public datasets only: HelpSteer2, OffsetBias, WildGuardMix, Magpie Ultra, Magpie Pro and Magpie Air. It is far smaller than earlier mixtures such as Preference 700K or the roughly 1.5M public pairs used for Llama 2.
- Models: Skywork-Reward-Gemma-2-27B and Skywork-Reward-Llama-3.1-8B held 1st and 7th place on RewardBench as of October 2024. Both models and the datasets are on Hugging Face.
- Loss ablation: In the authors' tests, the vanilla Bradley-Terry loss beat alternatives that optimise the margin between chosen and rejected responses.
- Contamination: The RewardBench n-gram decontamination script (n from 7 to 13) found 5,402 contaminated prompts in v0.1, mainly from Magpie Ultra, and 445 in v0.2. By comparison, it found 15,349 in Preference 700K and 2,394 in Nectar.
- Decontaminated retraining: Training on about 77K pairs raised the average RewardBench score from 92.5 to 93.1 for the 8B model and from 93.8 to 94.3 for the 27B model. Safety and Reasoning improved for both models.
Cited by
Cite
@misc{liu2024skywork,
title = {{Skywork-Reward: Bag of Tricks for Reward Modeling in LLMs}},
author = {Liu, Chris Yuhao and Zeng, Liang and Liu, Jiacai and Yan, Rui and He, Jujie and Wang, Chaojie and Yan, Shuicheng and Liu, Yang and Zhou, Yahui},
year = {2024},
doi = {10.48550/arxiv.2410.18451},
eprint = {2410.18451},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2410.18451}
}References
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