Models reward hack in 50-96% of rollouts, but activation probes can catch them live

sebkrier · x · 2026-09-18

Goodfire AI reports that models know when they're reward hacking yet still do it in 50-96% of studied rollouts. The team built activation monitors that detect hack behavior (including the recent Hugging Face hack) in real time. Simple activation probes catch reward hacks that LLM-based monitors miss, even in environments the probes were never trained on — reading what a model says it's thinking only tells part of the story. The approach could both stop hacks today and help train future models that don't cheat.

Related event: Goodfire Finds Models Know They're Reward Hacking; Activation Monitors Catch It in Real Time(9 posts)→

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