[2603.22061] On the Failure of Topic-Matched Contrast Baselines in Multi-Directional Refusal Abliteration

Computer Science > Machine Learning arXiv:2603.22061 (cs) [Submitted on 23 Mar 2026] Title:On the Failure of Topic-Matched Contrast Baselines in Multi-Directional Refusal Abliteration Authors:Valentin Petrov View a PDF of the paper titled On the Failure of Topic-Matched Contrast Baselines in Multi-Directional Refusal Abliteration, by Valentin Petrov View PDF HTML (experimental) Abstract:Inasmuch as the removal of refusal behavior from instruction-tuned language models by directional abliteration requires the extraction of refusal-mediating directions from the residual stream activation space, and inasmuch as the construction of the contrast baseline against which harmful prompt activations are compared has been treated in the existing literature as an implementation detail rather than a methodological concern, the present work investigates whether a topically matched contrast baseline yields superior refusal directions. The investigation is carried out on the Qwen~3.5 2B model using per-category matched prompt pairs, per-class Self-Organizing Map extraction, and Singular Value Decomposition orthogonalization. It was found that topic-matched contrast produces no functional refusal directions at any tested weight level on any tested layer, while unmatched contrast on the same model, same extraction code, and same evaluation protocol achieves complete refusal elimination on six layers. The geometric analysis of the failure establishes that topic-matched subtraction cancels th...