Synthetic Mixed Training: Scaling Parametric Knowledge Acquisition Beyond RAG

Seungju Han, Konwoo Kim, Chanwoo Park, Benjamin Newman, Suhas Kotha, Jaehun Jung, James Zou, Yejin Choi


Abstract
Synthetic data augmentation helps language models learn new knowledge in data-constrained domains. However, naively scaling existing synthetic data methods by training on more synthetic tokens or using stronger generators yields diminishing returns below the performance of RAG. To break the RAG ceiling, we introduce Synthetic Mixed Training, which combines synthetic QAs and synthetic documents. This leverages their complementary training signals, and enables log-linear improvements as both synthetic data volume and generator strength increase. This allows the model to outperform RAG by a 2.6% relative gain on QuaLITY, a long-document reading comprehension benchmark. In addition, we introduce Focal Rewriting, a simple technique for synthetic document generation that explicitly conditions document generation on specific questions, improving the diversity of synthetic documents and yielding a steeper log-linear scaling curve. On QuaLITY, our final recipe trains a Llama 8B model that outperforms RAG by 4.4% relatively. Across models and benchmarks (QuaLITY, LongHealth, FinanceBench), our training enables models to beat RAG in five of six settings, outperforms by 2.6%, and achieves a 9.1% gain when combined with RAG.
Anthology ID:
2026.findings-emnlp.438
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:
9193–9211
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.438/
DOI:
Bibkey:
Cite (ACL):
Seungju Han, Konwoo Kim, Chanwoo Park, Benjamin Newman, Suhas Kotha, Jaehun Jung, James Zou, and Yejin Choi. 2026. Synthetic Mixed Training: Scaling Parametric Knowledge Acquisition Beyond RAG. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 9193–9211, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Synthetic Mixed Training: Scaling Parametric Knowledge Acquisition Beyond RAG (Han et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.438.pdf