Identifying Interactions at Scale for LLMs

This blog post introduces SPEX and ProxySPEX, algorithms that use strategically selected ablations and sparse recovery from signal processing and coding theory to identify influential feature, data, and model-component interactions at scales far beyond prior methods, with ProxySPEX exploiting hierarchy to match SPEX using roughly 10x fewer ablations. The authors demonstrate the framework on sentiment analysis, a modified trolley problem with GPT-4o mini, CIFAR-10 data attribution with ResNet, and attention head pruning on MMLU, where a ProxySPEX-informed pruning strategy improved target-task performance. Code for both algorithms is available in the SHAP-IQ repository.