LLM Fine-tuning with an Unconstrained Fine-tuned Teacher

Jianhao Zhang, Ou Wu, Yi Du


Abstract
Fine-tuning large language models (LLMs) on a single target task requires balancing task adaptation with retention of prior capabilities. Existing teachers mainly guide preservation or transfer, but do not identify which target-task samples should be emphasized when fine-tuning must retain prior capabilities. We propose the **U**nconstrained **F**ine-tuned **T**eacher (**UFT**), shifting the teacher role from ”knowledge transfer” to ”value discovery”. UFT is obtained by unconstrained fine-tuning on the target task and then compared with the source model to identify high-value samples. These samples are upweighted during student fine-tuning and receive value-weighted UFT-guided distillation, allowing the student to prioritize task-critical signals while preserving prior capabilities. Experiments on Magicoder and MetaMathQA show that UFT improves the trade-off between target-task performance and prior-capability retention, while converging faster and more stably. By turning teacher behavior into sample-value discovery, UFT establishes a new teacher role for data-efficient fine-tuning.
Anthology ID:
2026.emnlp-main.1310
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
29812–29839
Language:
URL:
https://aclanthology.org/2026.emnlp-main.1310/
DOI:
Bibkey:
Cite (ACL):
Jianhao Zhang, Ou Wu, and Yi Du. 2026. LLM Fine-tuning with an Unconstrained Fine-tuned Teacher. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 29812–29839, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
LLM Fine-tuning with an Unconstrained Fine-tuned Teacher (Zhang et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.1310.pdf