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.