Component: L15H3_ATTN
Hook: blocks.15.attn.hook_z
Layer: 15
Head: 3
Role: Primary C-transfer head. At the final query position, this head selectively reads the third operand C and writes C-dependent information into the last-token residual stream. Its C edge is the load-bearing route. Corrupt-C patching moves the answer logits toward the C-corrupted answer, but this head alone does not fully overwrite the final prediction.
Additional note: Last survivor of iterative head pruning over layers 15-16. Single-head ablation in isolation drops accuracy 1.000 -> 0.758. Paper Fig. 5 shows it attends from the last token to the third operand C, routing C's value into the residual at the '=' position.