Learning New Facts with QLoRA: An Acquisition-Retention Frontier

Estelle Zheng, Sébastien Warichet, Emmanuel Helbert, Christophe Cerisara


Abstract
Parameter-efficient fine-tuning (PEFT) is often assumed to preserve pretrained capabilities because it updates only a small number of parameters. We show that this assumption depends strongly on adapter capacity. We study factual acquisition in a controlled OpenStreetMap-derived benchmark where Qwen3-4B must learn anonymized geographic relations while retaining unrelated capabilities. Comparing FFT with QLoRA ranks 8, 16, 32, and 64, we find that rank induces a clear acquisition–retention frontier. Low-rank QLoRA preserves OOD performance but acquires fewer facts, whereas higher ranks improve same-fact paraphrase generalization at increasing cost to unrelated benchmarks. FFT behaves as a conservative baseline: it retains general capabilities well, but does not reach the highest factual-acquisition regime. Distributional, weight-space, and spectral diagnostics mirror this behavioral trade-off, with higher-rank QLoRA moving farther from the pretrained model. A separate math adaptation experiment shows a weaker frontier, suggesting that the effect is most pronounced when adaptation must install new factual associations rather than reinforce skills already supported by pretraining.
Anthology ID:
2026.findings-emnlp.918
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
19397–19407
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.918/
DOI:
Bibkey:
Cite (ACL):
Estelle Zheng, Sébastien Warichet, Emmanuel Helbert, and Christophe Cerisara. 2026. Learning New Facts with QLoRA: An Acquisition-Retention Frontier. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 19397–19407, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Learning New Facts with QLoRA: An Acquisition-Retention Frontier (Zheng et al., Findings 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.findings-emnlp.918.pdf