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Compute-matched experiments found synthetic pre-pretraining never beat plain natural-language training, and models forgot what they learned

AspireAI community · arXiv
Synthetic pre-training corpora are sometimes proposed as a way to enlarge the effective pretraining dataset. Across four curricula - k-Dyck, neural cellular automata, declarative reference corpora and code - and three training regimes, including 881M parameters trained on 50B tokens, synthetic pre-pretraining never outperformed pure natural-language training. Reproducing a neural cellular automata result recovered a 5.4% perplexity improvement under the original weight-initialization scheme, but an alternative scheme helped the no-PPT baseline more, closing the gap. Models also forgot what they learned during PPT in subsequent natural-language training, though interleaving the same data throughout training prevented the forgetting without improving natural-language performance. The authors' scope is compute-matched small-scale runs, so the conclusion is about pre-pretraining as a distinct stage, not about synthetic data used inside ordinary training.
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