Title: Discern Truth from Falsehood: Reducing Over-Refusal via Contrastive Refinement
Primary area: foundation or frontier models, including LLMs
Keywords: Large Language Model, LLM Safety, Over-refusal, SafetyAlignment

Abstract: Large language models (LLMs) aligned for safety often suffer from over-refusal—the tendency to reject seemingly toxic or benign prompts by misclassifying them as toxic. This behavior undermines models' helpfulness and restricts usability in sensitive or nuanced contexts. While prior work has proposed mitigation strategies such as data augmentation and activation steering, these approaches often face a trade-off: reducing over-refusal typically degrades the model’s ability to reject genuinely harmful content.
We argue that this issue arises from the ambiguous influence of toxic and seemingly toxic prompts on the model’s learning dynamics. To address it, we introduce a preceding alignment stage, DCR: $\textbf{D}$iscernment via $\textbf{C}$ontrastive $\textbf{R}$efinement. Both theoretically and empirically, we demonstrate that contrastive refinement improves an LLM’s capacity to distinguish truly toxic prompts from superficially toxic ones. Evaluation across diverse benchmarks shows that our method effectively reduces over-refusal while preserving the safety benefits of alignment. Importantly, it achieves this with minimal degradation of general capabilities, offering a more principled and robust direction for safety alignment.

TL;DR: This paper introduces Discernment via Contrastive Refinement (DCR), a two-stage safety alignment method that uses contrastive learning to reduce over-refusal in LLMs while preserving safety and general abilities.