Fine-tuning a model quietly breaks its confidence scores, and 112 of 216 configurations got worse in ways the pre-fine-tune model could not predict
AspireAI community · arXiv (UncertaiNLP Workshop, EMNLP 2026)
Confidence scores and self-consistency are widely used for hallucination detection and selective prediction, but their behaviour after supervised fine-tuning was underexplored. Across 216 configurations on translation, question answering and mathematical reasoning, calibration degraded in 112 cases and improved in 104, so the effect is neither universal nor rare. The shift comes from factors beyond output quality, including proximity to the training distribution, and its direction cannot be anticipated from the pre-fine-tune model. The downstream consequence is that existing confidence metrics for generation cannot be deployed off-the-shelf after fine-tuning.
Read the story and explore more from the AspireAI community.
Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.