arXiv — NLP / Computation & Language · · 3 min read

Not All Synthetic Data Is Yours to Learn From

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Computer Science > Computation and Language

arXiv:2605.31126 (cs)
[Submitted on 29 May 2026]

Title:Not All Synthetic Data Is Yours to Learn From

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Abstract:Can a language model improve from plain text sampled from itself, with no prompts, no teacher, no verifier, and no reward model? Yes, but only when the synthetic corpus is compatible with the student, a relational property of the source-student pair rather than an intrinsic property of the data. We call this the latent capability resurfacing hypothesis: weak self-training can amplify capabilities already present in the pretrained model, but only under this compatibility condition. We study this in the minimal setting of prompt-free unconditional self-training, where base language models are fine-tuned on text generated from the BOS token alone, with no task specification or external supervision. We report three findings. First, synthetic utility is relational rather than intrinsic: self-generated data is the most effective source, same-lineage transfer outperforms stronger but differently trained sources, and cross-family transfer is substantially weaker. Second, common intrinsic proxies fail: neither benchmark-level semantic similarity nor average per-token likelihood under the student predicts which corpora help. Third, this regime produces a surprising byproduct. In controlled Pythia experiments, capability and verbatim memorization decouple: benchmark utility is preserved or improved while held-out exact-match extraction drops by over 95 percent, with no forget set, privacy objective, or targeted unlearning. Together, these results suggest that prompt-free self-training works by amplifying what the student already knows, not by importing structure from the data. They also reveal a regime in which capability and verbatim memorization can be separated without any explicit unlearning objective.
Subjects: Computation and Language (cs.CL); Artificial Intelligence (cs.AI); Machine Learning (cs.LG)
Cite as: arXiv:2605.31126 [cs.CL]
  (or arXiv:2605.31126v1 [cs.CL] for this version)
  https://doi.org/10.48550/arXiv.2605.31126
arXiv-issued DOI via DataCite (pending registration)

Submission history

From: Sina Alemohammad [view email]
[v1] Fri, 29 May 2026 10:34:11 UTC (216 KB)
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