May 10, 2026
MonitoringBench shows refined covert attacks cut an Opus 4.5 monitor's catch rate from 95% to 60%
Jotautaitė, Martinez, Matthews and Tracy (two listed as independent, Tracy at Redwood Research) build a semi-automated red-teaming pipeline in the BashArena control setting, where agents covertly pursue side tasks such as firewall backdoors, privilege escalation, credential exfiltration and malware download. MonitoringBench's 2,644 attack trajectories lowered a Claude Opus 4.5 monitor's catch rate at 1% false positives from 94.9% on directly elicited attacks to 60.3% on refined ones.