Pre-DPO: Improving Data Utilization in Direct Preference Optimization
  Using a Guiding Reference Model
Authors: name: Junshu Pan; name: Wei Shen; name: Shulin Huang; name: Qiji Zhou; name: Yue Zhang
Published: 2025-04-22 12:39:30

Abstract: Direct Preference Optimization (DPO) simplifies reinforcement learning from
human feedback (RLHF) for large language models (LLMs) by directly optimizing
human preferences without an explicit reward model. We find that during DPO
training, the reference model plays the role of a data weight adjuster.
However, the common practice of initializing the policy and reference models
identically in DPO can lead to inefficient data utilization and impose a
performance ceiling. Meanwhile, the lack of a reference model in Simple
Preference Optimization (SimPO) reduces training robustness and necessitates
stricter conditions to prevent catastrophic forgetting. In this work, we
propose Pre-DPO, a simple yet effective DPO-based training paradigm that
enhances preference optimization performance by leveraging a guiding reference
model. This reference model provides foresight into the optimal policy state
achievable through the training preference data, serving as a guiding mechanism
that adaptively assigns higher weights to samples more suitable for the model
and lower weights to those less suitable. Extensive experiments on AlpacaEval
2.0 and Arena-Hard v0.1 benchmarks demonstrate that Pre-DPO consistently
improves the performance of both DPO and SimPO, without relying on external
models or additional data.