Open Weights vs. Open Source
Definition
Open weights means a provider makes the trained model parameters available for download. Open source additionally means that training code, data specification and a licence are available that explicitly permit redistribution, modification and commercial use — in the spirit of the Open Source Initiative's definitions and the Open Source AI Definition (OSAID).
Noise — Signal
When a vendor advertises "open-source AI", they almost always mean open weights with a restricted licence. This isn't a semantic detail. It decides whether a model is auditable, can be operated on-premises, may be fine-tuned, and whether the supply chain can be documented for DORA, MaRisk and the AI Act. A licence that excludes commercial use above a certain size or restricts use cases is not open source — even if the model is marketed that way.
The right question
Not: "Is the model open source?" But: "Which components — weights, code, training data, licence terms — are available under which conditions, and is that enough for our regulatory evidence obligations and our exit strategy?"