Any-Depth Alignment: Unlocking Innate Safety Alignment of LLMs to Any-Depth

Jiawei Zhang, Andrew Estornell, David D. Baek, Bo Li, Xiaojun Xu

Keywords: Large Language Models, Any-Depth Alignment, Deep-prefill attacks, Safety token, Inference-time defense

TL;DR: We propose Any-Depth Alignment (ADA), an inference-time method that reactivates LLM safety at any generation depth, blocking deep adversarial attacks while preserving benign utility.

Abstract: Large Language Models (LLMs) exhibit strong but shallow alignment: they directly refuse harmful queries when a refusal is expected at the very start of an assistant turn, yet this protection collapses once a harmful continuation is underway (either through the adversarial attacks or via harmful assistant-prefill attacks). This raises a fundamental question: Can the innate shallow alignment in LLMs be unlocked to ensure safety at arbitrary generation depths? To achieve this goal, we propose Any-Depth Alignment (ADA) an effective inference-time defense with negligible overhead. ADA is built based on our observation that alignment is concentrated in the assistant header tokens through repeated use in shallow-refusal training, and these tokens possess the model’s strong alignment priors. By reintroducing these tokens mid-stream, ADA induces the model to reassess harmfulness and recover refusals at any point in generation. Across diverse open-source model families (Llama, Gemma, Mistral, Qwen, DeepSeek, and gpt-oss), ADA achieves robust safety performance without requiring any changes to the base model's parameters. It secures a near-100% refusal rate against challenging adversarial prefill attacks ranging from dozens to thousands of tokens. Furthermore, ADA reduces the average success rate of prominent adversarial prompt attacks (such as GCG, AutoDAN, PAIR, and TAP) to below 3%. This is all accomplished while preserving benign utility with minimal over-refusal and maintaining resilience even after the base model undergoes subsequent instruction tuning.

Submission Number: 99