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arXiv · 2610.20086

AFCS: Atomic-Fact-Conditioned Synthesis for Factual Knowledge Pretraining

Yunhao Wang·Feng Zhang·Tinghao Yu·Xing Wu·Jiang Zhou
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Abstract

Synthetic data is increasingly used in language-model pretraining. Existing knowledge-corpus synthesis pipelines, including WRAP and Nemotron-CC, usually take a source passage or document segment as input and generate rewritten or QA-style samples from that text. This can improve surface form and prompt diversity, but it does not explicitly require fine-grained source facts -- especially secondary entities, list/table entries, and precise temporal attributes -- to appear in the synthesized corpus. We propose AFCS (Atomic-Fact-Conditioned Synthesis), a pipeline that first extracts source-supported atomic facts and then uses each retained fact to drive generation. AFCS uses structure-aware extraction over the document tree, source-grounded verification, local context expansion, and multi-format generation. In continued-pretraining experiments with OLMo-3-7B and a 32B base on the same FineWiki source corpus, AFCS outperforms WRAP and Nemotron-CC on SimpleQA, SimpleQA Verified, PopQA, and HotpotQA. Granularity ablations show that fact-level synthesis improves over chunk-level, paragraph-level, and entity-level synthesis; and a 100B-token mid-training integration improves factual benchmarks and raises the 12-task general benchmark average by +1.09.

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Yunhao Wang, Feng Zhang, Tinghao Yu, Xing Wu, Jiang Zhou. 2026-10-14. AFCS: Atomic-Fact-Conditioned Synthesis for Factual Knowledge Pretraining. https://arxiv.org/abs/2610.20086

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