Open weight is not open source

2026-08-11

Open Weight: access to model parameters.

Open Source: access to the foundational training data, code, and infrastructure.

Open weight is not open source.

In the past month I've noticed a concerning misuse of the term "open source" to describe what is really "open weight".

• open-weight models labelled open-source¹².
• softened variants like “open source the weights”³⁴.
• benchmarks listing open-weight models as open source⁵.
• The press have begun to adopt the same lingo⁶⁷.

This conflation is dangerous, for various reasons:

• false trust - readers assume a level of transparency that does not exist such as expectations of reproducibility and auditability.
• obscures the real source of power - data, training, and infrastructure, while maintaining a veil of openness.
• erodes the true meaning of OSS.
• makes it harder to recognize and reward projects that are actually open.
• causes confusion in less expert audiences including policy makers who reasonably assume that open source means something else.

What should we do?

Use precise language. Say open weight if it's open weight, say open source if it's open source.

Call it out when you see it. Leave a comment on HN/Lobste.rs or other platform.

Open weight models are useful. They are just not open source.