Component: L28H18_ATTN
Hook: blocks.28.attn.hook_z
Layer: 28
Head: 18
Role: L28H18 attention head's output is the strongest late-attention projection toward the correct answer, but its attention is mostly on <BOS> and positional tokens rather than operands. Removing it does not reduce accuracy, so this answer-related signal is not needed by itself in the full circuit.
Additional note: L28H18 is the strongest paper-named late-attention lens hit. Evidence for answer-related output: per-head logit lens ranks it 1/480 over layers 17-31. Evidence that it is not primarily reading operands: at the last query position, attention mass is BOS = 0.445 and operand sum A+B+C = 0.102. The remaining non-BOS mass is concentrated more on positional anchors such as '=' than on operands. Evidence against isolated necessity: when L28H18 and the other high-lens late attention heads are zeroed cumulatively, accuracy remains 1.0, including after L28H18 is removed. This matches the paper's Sec. 4.5 and Appendix A.4 claim that these answer-predicting heads show a BOS-sink pattern rather than an interpretable operand-reading pattern.