Domain Mixture Design via Log-Likelihood Differences for Aligning Language Models with a Target Model

Ryo Kishino, Riku Shiomi, Hiroaki Yamagiwa, Momose Oyama, Hidetoshi Shimodaira


Abstract
Instead of directly distilling a language model, this study addresses the problem of aligning a base model with a target model in distribution by designing the domain mixture of training data for pretraining or continued pretraining as a fixed training recipe. We propose a method for determining domain weights by viewing models as points in log-likelihood space and aligning the training update direction with the direction toward the target model. Experiments with NanoGPT show that the proposed method consistently reduces the KL divergence between the trained base model and the target model relative to training with Pile-original weighting. Although knowledge distillation remains more effective when available, the proposed method achieves meaningful alignment, and downstream task performance also tends to become closer to that of the target model.
Anthology ID:
2026.findings-emnlp.1431
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:
30483–30499
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.1431/
DOI:
Bibkey:
Cite (ACL):
Ryo Kishino, Riku Shiomi, Hiroaki Yamagiwa, Momose Oyama, and Hidetoshi Shimodaira. 2026. Domain Mixture Design via Log-Likelihood Differences for Aligning Language Models with a Target Model. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 30483–30499, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Domain Mixture Design via Log-Likelihood Differences for Aligning Language Models with a Target Model (Kishino et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.1431.pdf