What Carries Forward? Pretraining Disclosure Across Language Model Releases
Understanding how language models were pretrained requires information about their data, processing procedures, and computational resources. However, it remains unclear whether successive releases preserve or expand earlier disclosure. We conduct a document-based audit of 41 model entries from 17 families using 24 pretraining-related indicators from the 2025 Foundation Model Transparency Index (FMTI). We examine overall scores and indicator profiles, tracking gains, losses, and retained disclosures across 24 adjacent comparisons in ten families. Scores decrease in 11 comparisons, increase in six, and remain unchanged in seven, with 38 indicator losses and 28 gains overall. Stable or improving scores can conceal losses: OLMo-2 and OLMo-3 receive identical totals despite three gains and three losses, while Llama-3.1 improves over Llama-2 while losing credit for two data-related criteria. Gaps also persist in corpus composition and training compute. These findings show that later releases do not consistently preserve earlier pretraining disclosure and motivate documentation that explicitly identifies changes and the applicability of inherited information.