Tracking Universal Features Through Fine-Tuning and Model Merging

Niels Nielsen Horn, Desmond Elliott


Abstract
We study how features emerge, disappear, and persist across models fine-tuned on different domains of text. More specifically, we start from a base one-layer Transformer language model that is trained on a combination of the BabyLM corpus, and a collection of Python code from The Stack. This base model is adapted to two new domains of text: TinyStories, and the Lua programming language, respectively; and then these two models are merged using these two models using spherical linear interpolation. Our exploration aims to provide deeper insights into the stability and transformation of features across typical transfer-learning scenarios using small-scale models and sparse auto-encoders.
Anthology ID:
2025.repl4nlp-1.2
Volume:
Proceedings of the 10th Workshop on Representation Learning for NLP (RepL4NLP-2025)
Month:
May
Year:
2025
Address:
Albuquerque, NM
Editors:
Vaibhav Adlakha, Alexandra Chronopoulou, Xiang Lorraine Li, Bodhisattwa Prasad Majumder, Freda Shi, Giorgos Vernikos
Venues:
RepL4NLP | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
26–37
Language:
URL:
https://preview.aclanthology.org/fix-sig-urls/2025.repl4nlp-1.2/
DOI:
Bibkey:
Cite (ACL):
Niels Nielsen Horn and Desmond Elliott. 2025. Tracking Universal Features Through Fine-Tuning and Model Merging. In Proceedings of the 10th Workshop on Representation Learning for NLP (RepL4NLP-2025), pages 26–37, Albuquerque, NM. Association for Computational Linguistics.
Cite (Informal):
Tracking Universal Features Through Fine-Tuning and Model Merging (Horn & Elliott, RepL4NLP 2025)
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PDF:
https://preview.aclanthology.org/fix-sig-urls/2025.repl4nlp-1.2.pdf