Confidence Drift During Task-Specific Language Model Fine-Tuning

Soham Tripathy


Abstract
Task-specific fine-tuning can change not only what a language model predicts, but also how confident it is in those predictions. We study confidence and accuracy drifts throughout LoRA fine-tuning of seven decoder-only language models spanning multiple families and scales. Models are fine-tuned on AG News and evaluated at intermediate checkpoints on the source task and five untouched cross-task benchmarks. We find that cross-task accuracy generally remains stable or degrades, while confidence increases on both correct and incorrect predictions. Across many settings, confidence follows a non-monotonic trajectory: after an early transient and a relatively stable middle stage, it rises again late in training, coinciding with increasing train–validation NLL divergence. Our results show that accuracy-only evaluation can miss confidence drifts introduced by task-specific fine-tuning.
Anthology ID:
2026.uncertainlp-main.42
Volume:
The Proceedings of the Third Workshop on Uncertainty-Aware NLP
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Wilker Aziz, Jonathan Berant, Bryan Eikema, Evgenia Ilia, Marie-Catherine de Marneffe, Barbara Plank, Artem Shelmanov, Swabha Swayamdipta, Jörg Tiedemann, Artem Vazhentsev, Raúl Vázquez, Chrysoula Zerva
Venues:
UncertaiNLP | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
693–703
Language:
URL:
https://aclanthology.org/2026.uncertainlp-main.42/
DOI:
Bibkey:
Cite (ACL):
Soham Tripathy. 2026. Confidence Drift During Task-Specific Language Model Fine-Tuning. In The Proceedings of the Third Workshop on Uncertainty-Aware NLP, pages 693–703, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Confidence Drift During Task-Specific Language Model Fine-Tuning (Tripathy, UncertaiNLP 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.uncertainlp-main.42.pdf