Exemplar Partitioning for Mechanistic Interpretability
This work proposes an unsupervised Example Partitioning (EP) method to efficiently construct interpretable and computationally lightweight feature dictionaries for analyzing the internal mechanisms of large language models. EP leverages real samples from streaming activation data as Voronoi region anchors, eliminating the need to predefine dictionary size, and uniquely employs observed activations directly as both intervention directions and region representatives. This enables feature alignment across layers, models, and training stages while inherently supporting out-of-distribution detection. By integrating distance-threshold leader clustering with causal interventions, EP achieves superior performance on Gemma-2-2B, surpassing GemmaScope SAE’s AxBench AUROC (0.881) at only one-thousandth of the computational cost, retaining 97% probe accuracy, and exhibiting high consistency with SAE features in 20% of its regions.