When Do Internal Probes Beat Reading the Answer? Miscalibrated Readouts and Behavior-Concealed Knowledge in Language Models
2026-09-07 12:00Science🔥 42.2 heat score
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A study on a 0.6B parameter language model found that when verifying 1,200 logical conclusions, its behavior could not distinguish between true and false (accuracy was only 50%). However, linear probes could accurately read the correct judgments in the hidden states (AUC 0.96). The study indicated that the dominant factor causing judgment loss was a single scalar: the judgment information along the alignment direction in the model’s logits was intact (AUC 0.89), but it was erased by a saturation decision threshold with an offset of +4.6 standard deviations. This diagnosis is universal; in experiments with 90 semantic label configurations and across models, behavior accuracy collapsed in a single-function relationship with the threshold offset (Spearman -0.93), while marginal rankings were less affected. The study proposed an actionable solution: by correcting with a single parameter, calibrating marginal decoding, or adjusting prompts, the threshold can be re-centered, improving the behavior accuracy of the 0.6B model from 50% to 81%, and restoring the 8B model to 94%.