Component: L26H3_ATTN
Hook: blocks.26.attn.hook_z
Layer: 26
Head: 3
Role: L26H3 attention head's output points toward the correct answer in projection tests, but its attention mostly goes to the <BOS> token rather than the operand tokens. Removing this head does not reduce accuracy, so this answer-related signal is not needed by itself in the full circuit.
Additional note: L26H3 is a paper-named BOS-attention-sink case. Evidence for answer-related output: per-head logit lens ranks it 2/480 over layers 17-31, with top-1 = 0.162 and top-3 = 0.394. Evidence that it is not reading operands: at the last query position, attention mass is BOS = 0.587 and operand sum A+B+C = 0.027. Evidence against isolated necessity: when L26H3 and the other high-lens late attention heads are zeroed cumulatively, accuracy remains 1.0, including after L26H3 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.