Before it
Open corpora existed but the pipelines that produced them were partly undocumented.
The problem
Without the tooling and decisions, you cannot audit or rebuild a corpus.
What it introduced
Three trillion tokens released with the full curation toolkit and documented design decisions.
Why it matters
It made pretraining data auditable, which matters for bias, contamination and copyright questions.
What modern models inherit
Data provenance as a publishable artefact.
What came next
OLMo trained on it; FineWeb pushed the open-data quality bar further.