You download a weights file. It runs on your machine. The model answers your prompts and nothing leaves the building. It feels like freedom, and a lot of the time it is. But the word stamped on it, “open,” is doing more work than it can carry.
Open weights and open source sound like the same claim. They are not. One is about whether you can get the file. The other is about what you are allowed to do with it. The gap between those two is where people get surprised.
What “open weights” actually means
Open weights means the trained model is available to download and run. That is a real and useful thing. You get the actual file, you can run it offline, you can fine-tune it, and you are not renting access through an endpoint.
But “available to download” is not the same as “free to use however you like.” A weights file arrives with a license, and the license is the part that decides what you can actually do. Some open-weights licenses are genuinely permissive. Others are not. The download is identical either way, which is exactly why the word hides the difference.
Three things “open” can quietly leave out
Read the license, not the headline. Three things tend to go missing.
Use restrictions. An open-weights model can ship with a license that limits what you are allowed to use it for. Certain uses are forbidden, certain industries are excluded, and past a certain scale you may need a separate agreement. That is a real constraint, and it is not what most people mean by open source.
The training data. Open weights gives you the finished model, not the recipe. The data it was trained on, the steps that produced it, and the code that did the training are frequently withheld. You can run the result. You cannot reproduce it or fully inspect how it came to be.
OSI-open licensing. “Open source” has a specific meaning, defined by the Open Source Initiative, that includes the freedom to use the thing for any purpose. Plenty of open-weights licenses do not meet that bar. They are custom licenses written by the model’s makers, and they keep restrictions that an OSI-approved license would not allow. The model can be downloadable and still not be open source in the established sense of the term.
Why this matters in practice
For a lot of work, none of this bites. You run the model, it does the job, and the license never enters the room.
It enters the room the moment money or scale shows up. If you are building a product on top of a model, putting it in front of clients, or running it at volume, the license is not a formality. It decides whether you are allowed to do the thing you just built. A clause you skimmed can be the difference between a tool you own and a tool you have to tear out later.
The honest counterpoint
Open weights is still a real gift, and this is not a reason to dismiss it. A downloadable model you can run offline and fine-tune is worlds better than an API you can only rent. The freedom to inspect, to run privately, and to not depend on a vendor’s uptime is genuine, even under a restrictive license. Plenty of teams will never hit the limits in the fine print, and for them the distinction is academic.
The point is smaller and sharper than “open weights is bad.” It is: do not let the word “open” do your reading for you. The license is a short document. It tells you exactly what you have.
Next time you pull a model, open its license before its first prompt. Read the part about what you may and may not do. Curious about these things. You should be too.
Harness your curiosity.
— Stridenote · № 007