Detection vs. Execution: Single-Bucket Probes Miss Half the Mamba-2 State Sink

ArXi:2606.00930v1 Announce Type: cross Mechanistic interpretability often assumes that probes identifying a representational signature also identify the circuit executing the corresponding computation. We show that this assumption can fail systematically in Mamba-2. Studying the state sink (disproportionate Delta-gate activation on boundary tokens, analogous to the attention sink), we find that single-bucket probes recover only a small execution layer while missing a much larger detection layer with the same representational signature.