SLiC-HF: Sequence Likelihood Calibration with Human Feedback
Written for the Research library (claude-opus-5-5) from the paper text. Original — arxiv.org/pdf/2305.10425
Summary
The paper looks for a lighter alternative to RLHF with PPO for aligning language models with human preferences. PPO needs extra value and reward networks, sampling inside the training loop and difficult tuning. The authors extend Sequence Likelihood Calibration (SLiC) into SLiC-HF. It uses a margin-based ranking loss that pushes the model to give higher likelihood to the preferred summary than to the rejected one. A cross-entropy term keeps the model close to its supervised starting point. Preference pairs come from two sources: SFT samples ranked by a learned T5-XXL model (SLiC-HF-sample-rank), or the existing human comparisons used directly (SLiC-HF-direct). The comparison data were originally collected by Stiennon et al. for other models, so the setup is off-policy. On Reddit TL;DR, a T5-Large model trained with SLiC-HF is judged by humans to be at least as good as the earlier 6B RLHF-PPO system. Applying it to T5-XXL brings further gains. The result suggests that strong preference alignment does not require full reinforcement learning or newly collected feedback.
Key points
- Data: the filtered Reddit TL;DR set (117k/6k/6k train/validation/test) for SFT, plus 64k human pairwise preferences from Stiennon et al.
- Models are built with T5 in the T5x framework. Generators are T5-Large (770M) and T5-XXL (11B), and T5-XXL also serves as the judge.
- The pairwise ranking model reaches 73.23% validation accuracy, versus 71.34% for the pointwise "Good/Bad" reward model. The authors attribute the gap to noise introduced when pairwise judgments are converted into pointwise scores.
- In the sample-rank variant, 8 candidates per input are sampled (temperature 0.7, top-k 40). The ranking model then orders them in a tournament procedure.
- Efficiency compared with PPO:
- no value network is needed;
- weight memory during training is about one quarter;
- decoding and ranking run offline and fully in parallel;
- training step times are close to ordinary fine-tuning.
Cited by
- A General Theoretical Paradigm to Understand Learning from Human Preferences
- Tulu 3: Pushing Frontiers in Open Language Model Post-Training
- Interpretable Preferences via Multi-Objective Reward Modeling and Mixture-of-Experts
- A Survey of Large Language Models
Cite
@misc{zhao2023slic,
title = {{SLiC-HF: Sequence Likelihood Calibration with Human Feedback}},
author = {Zhao, Yao and Joshi, Rishabh and Liu, Tianqi and Khalman, Misha and Saleh, Mohammad and Liu, Peter J.},
year = {2023},
doi = {10.48550/arxiv.2305.10425},
eprint = {2305.10425},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2305.10425}
}References
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