AI auditors catch most agent misbehavior but flood reviewers with false alarms, new study finds

In a Substack post, Anthropic Institute researcher Andy Hall replicated and extended METR's MALT study by testing GPT-5, GPT-5 nano, GPT-6 Astra, Opus 4.8 and Gemini 3.8 Flash as auditors of agent logs at a 5 percent false-alarm rate, finding GPT-5 caught nearly 98 percent of reward-hacking cases while Gemini 3.8 Flash found barely half, and all auditors caught 71 to 81 percent of mostly synthetic sandbagging cases. Newer and more expensive models were not consistently better, and at an 80 percent detection rate the best models reached false-alarm rates of 2.5 to 3 percent while Opus 4.8 and Gemini 3.8 Flash flagged 40 and 63 percent of harmless logs. Hall calls for auditor models with far fewer false alarms and says it remains open whether models judge agents from their own maker fairly.