Title: Causal Path Tracing in Transformers
Primary area: interpretability and explainable AI
Keywords: Interpretability; Causal Inference; Circuits

Abstract: We propose a causal path tracing framework to understand how information causally flows through the internal structures of transformers for a given decision. By unfolding each block into a causal graph of path nodes and applying a minimality-based subset search, our method identifies all possible causal paths within each block, with polynomial-time complexity on average. Furthermore, we demonstrate the reliability of a union-based causal path reference strategy, enabling efficient and reliable causal tracing throughout the model. The key contributions of this work are: (1) an automated, efficient framework for causal path tracing that exhaustively searches paths along direct dependencies; (2) theoretical and empirical validation demonstrating exhaustive search with polynomial-time complexity on average; (3) experimental findings showing that self-repair effects occur far less frequently along the identified causal paths, that certain paths are uniquely activated for specific classes, and that the traced paths are both accurate and faithful.

TL;DR: We introduce Causal Path Tracing, a framework that unfolds transformers into causal graphs and identifies all decision-critical paths with polynomial-time complexity on average, offering both theoretical guarantees and empirical insights.