How do LLMs Compute Verbal Confidence
- URL: http://arxiv.org/abs/2603.17839v1
- Date: Wed, 18 Mar 2026 15:31:43 GMT
- Title: How do LLMs Compute Verbal Confidence
- Abstract summary: We show that verbal confidence reflects automatic, sophisticated self-evaluation -- not post-hoc reconstruction.<n>These findings have implications for understanding metacognition in LLMs and improving calibration.
- Score: 20.456986780602964
- License: http://creativecommons.org/licenses/by/4.0/
- Abstract: Verbal confidence -- prompting LLMs to state their confidence as a number or category -- is widely used to extract uncertainty estimates from black-box models. However, how LLMs internally generate such scores remains unknown. We address two questions: first, when confidence is computed - just-in-time when requested, or automatically during answer generation and cached for later retrieval; and second, what verbal confidence represents - token log-probabilities, or a richer evaluation of answer quality? Focusing on Gemma 3 27B and Qwen 2.5 7B, we provide convergent evidence for cached retrieval. Activation steering, patching, noising, and swap experiments reveal that confidence representations emerge at answer-adjacent positions before appearing at the verbalization site. Attention blocking pinpoints the information flow: confidence is gathered from answer tokens, cached at the first post-answer position, then retrieved for output. Critically, linear probing and variance partitioning reveal that these cached representations explain substantial variance in verbal confidence beyond token log-probabilities, suggesting a richer answer-quality evaluation rather than a simple fluency readout. These findings demonstrate that verbal confidence reflects automatic, sophisticated self-evaluation -- not post-hoc reconstruction -- with implications for understanding metacognition in LLMs and improving calibration.
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