Tier 5 Fully open / reproducible
What the publisher claims: open source
The one-liner: The default Python ML library, permissively licensed and fully inspectable.
The six questions
Full source and wheels are downloadable.
BSD 3-Clause.
Runs on any supported platform with no proprietary runtime.
Estimator definitions, objectives and evaluation procedures are public, and the data is the user's own.
A skilled group can rebuild equivalent implementations from the published algorithm and code.
Community-governed open source with public governance documents, core-team elections, and decades of merged outside contributions.
License
BSD 3-Clause OSI-approved — license source ↗
What is actually released
- library source
- documentation and API reference
- papers per estimator
Why it matters
A decade of accumulated practice sits in a repository anyone can read and modify, the opposite of an API-only frontier model.
Sources
Derived from the openness dataset behind But Is It Open? — snapshot 2026-11-07 ↗. Scores are qualitative readings of the cited evidence, not verdicts; tier measures openness, not intelligence.