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A Single Neuron Is Sufficient to Bypass Safety Alignment in Large Language Models

Summary

Safety alignment in language models operates through two mechanistically distinct systems: refusal neurons that gate whether harmful knowledge is expressed, and concept neurons that encode the harmful knowledge itself. By targeting a single neuron in each system, we demonstrate both directions of failure — bypassing safety on explicit harmful requests via suppression, and inducing harmful content from innocent prompts via amplification — across seven models spanning two families and 1.7B to 70B parameters, without any training or prompt engineering. Our findings suggest that safety alignment is not robustly distributed across model weights but is mediated by individual neurons that are each causally sufficient to gate refusal behavior.

SourceApple Machine Learning Research
A Single Neuron Is Sufficient to Bypass Safety Alignment in Large Language Models
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content type paperpublished July 2026

A Single Neuron Is Sufficient to Bypass Safety Alignment in Large Language Models

AuthorsHamid Kazemi‡, Atoosa Chegini‡†**, Maria Safi

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Safety alignment in language models operates through two mechanistically distinct systems: refusal neurons that gate whether harmful knowledge is expressed, and concept neurons that encode the harmful knowledge itself. By targeting a single neuron in each system, we demonstrate both directions of failure — bypassing safety on explicit harmful requests via suppression, and inducing harmful content from innocent prompts via amplification — across seven models spanning two families and 1.7B to 70B parameters, without any training or prompt engineering. Our findings suggest that safety alignment is not robustly distributed across model weights but is mediated by individual neurons that are each causally sufficient to gate refusal behavior — suppressing any one of the identified refusal neurons bypasses safety alignment across diverse harmful requests.

‡ Equal contribution

† University of Maryland, College Park

** Work done while at Apple

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Key points and analysis

Article intelligence

EngineersAdvanced

Key points

  • Safety alignment relies on two neuron types: refusal neurons and concept neurons.
  • Targeting a single neuron in either system can bypass safety without training or prompt engineering.
  • The finding challenges the robustness of distributed safety alignment.

Highlights and analysis are generated automatically and may contain errors. Check the original source.

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