Probe detection traced to a single attention head reading the user token's hidden state

Sauers_ · x · 2026-10-18

Activation-swap experiments show the model detects probes via tiny differences in the user token's hidden state: swapping activations at that token alone (99% of effect), or one head's output (head 6, layer 35), fully reproduces the behavior change.

Related event: Study shows LLMs can learn to detect activation probes and tell training from deployment(15 posts)→

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