Path Patching

Path patching is the causal method that patches specific source-to-target internal paths to isolate directional information flow - it provides finer-grained circuit analysis than broad component-level patching.

What Is Path patching?

• Definition: Intervenes on selected edges between components rather than whole activations.
• Directionality: Tests whether information moves through a hypothesized path to affect output.
• Resolution: Can separate competing pathways that converge on similar downstream nodes.
• Computation: Often requires careful instrumentation of intermediate forward-pass tensors.

Why Path patching Matters

• Circuit Precision: Improves confidence in specific causal route identification.
• Mechanism Clarity: Distinguishes direct pathways from correlated side channels.
• Intervention Targeting: Supports precise model edits with reduced collateral effects.
• Research Depth: Enables detailed decomposition of multi-step reasoning circuits.
• Method Rigor: Provides stronger evidence than coarse ablation in complex behaviors.

How It Is Used in Practice

• Hypothesis First: Define candidate source-target paths before running patch experiments.
• Control Paths: Include negative-control routes to detect false positives.
• Replicability: Re-test influential paths across prompt families and random seeds.

Path patching is a fine-grained causal instrument for transformer circuit mapping - path patching is most effective when used with explicit controls and clearly defined path hypotheses.