Beyond One-Hot Replay: Self-Distillation Reduces Target Variance in Continual Pre-Training

Peng Lu, Sijie Dong, Xiaoyun Feng, Xuanwei Hu, Xin Zhang


Abstract
Continual pre-training (CPT) adapts a pretrained language model to a target domain, but it often degrades general capabilities even when general-data replay is used to mitigate forgetting. We revisit this failure through replay supervision: prior CPT replay mainly tunes data mixtures and token budgets while applying one-hot next-token prediction (NTP) uniformly to domain and replay tokens. This target is natural for learning domain text, but on replay tokens it introduces target variance: it is a noisy, corpus-dependent proxy for preserving the frozen base model’s conditional behavior. We study self-distilled replay: domain tokens keep NTP, while replay tokens are trained to match the frozen base model distribution. Diagnostics show that this target substitution lowers target error, produces more directionally consistent replay gradients, and reduces base-behavior drift. Empirically, self-distilled replay improves the SmolLM3 domain–general trade-off over matched NTP replay across diverse token budgets and replay ratios. It also remains effective for Qwen3 models whose pretraining mixtures are unavailable: under the same mismatched, non-source replay setting, it improves both general score and PubMedQA in all eight matched comparisons. Overall, these results suggest supervising CPT replay to preserve base behavior, rather than fit empirical next tokens, as a way to reduce target variance.
Anthology ID:
2026.findings-emnlp.1299
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:
27473–27491
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.1299/
DOI:
Bibkey:
Cite (ACL):
Peng Lu, Sijie Dong, Xiaoyun Feng, Xuanwei Hu, and Xin Zhang. 2026. Beyond One-Hot Replay: Self-Distillation Reduces Target Variance in Continual Pre-Training. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 27473–27491, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Beyond One-Hot Replay: Self-Distillation Reduces Target Variance in Continual Pre-Training (Lu et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.1299.pdf