Edit: as bayindirh noted, according to OSI's definition, I am completely incorrect about redistribution of modifications.
Current state is detrimental to both Free/Open Software and AI ecosystems at the same time.
My point is that open weights exists somewhere on the spectrum between closed source and open source, and imo much closer to open source than closed.
As evidence, see the thousands of open-weight model derived models on hugging face.
Creative Commons licenses are a spectrum from CC BY to CC BY-NC-ND. All six licenses offer different freedoms and requirements about the work licensed.
As I said in another comment, Open meant that you can buy an interface to the thing you are interested in. Nothing like Open Source or Free Software of today, and Open Weights lean to the former than the latter, this is what rubs the people the wrong way (incl. me).
A better term would be weights-available. Do not create false assumptions about so-called openness of a model, and is akin to sharing an object file which you can compile into something but its source is not available to start from scratch.
Nuances matter, that's true, but the packaging of the facts also matter. A good example is, again, XKCD's comic titled Free [0]. Open weights are open as the open of 2000s commercial software, maybe with a free SDK, but the labeling is deceiving on purpose.
This just isn’t true. 2000s commercial software you buy under a restrictive license, and then extend using an sdk. You can’t modify or distribute the code only your plugin or extension. Open weight models you freely download and modify and extend using open source tools, and create derivative works. The licenses tend to be very permissive (e.g. Apache 2.0 https://huggingface.co/Qwen/Qwen3.8-27B/blob/main/LICENSE)
Perhaps you are not aware of the thousands of derivative models that have been created based on open weight models? Ones tuned for this or that task, expanded, hacked apart.
> akin to sharing an object file which you can compile into something
I see what you are getting at, but modifying object files isn’t practical or simple or commonly done. A model that’s been post trained isn’t the old model with a lump of new code attached to it. The weights have been irreversibly altered and it’s a new thing now. A derivative work.
My contention is that model weights are a form of source code. They the software AND a modifiable thing, closer to minified js than a binary blob. Less flexible than the full training data would be, in some ways, but more useful in others (unless you have a large data center at your disposal). Would you consider something closed source if it had a bunch of generated code, but didn’t include the code used to generate the generated code? I would.