Evidence-Guided Unknown Rejection for High-Confidence Near-Known Unknowns

ArXi:2605.17818v1 Announce Type: new Open-set recognition systems face a neglected failure mode: high-confidence near-known unknowns, which lie outside the known label set but are close enough to known classes that a closed-set classifier accepts them with high confidence. We show that this failure is widespread across scalar-threshold methods, including recent post-hoc detectors, and that stronger encoders can amplify rather than remove the risk.