An open weights model is an AI model whose weights, the numbers adjusted during training, are available to download. You can run it with the right hardware and software, within what its license allows. Open weights alone do not make a model open source.
A question from the app. Pick an answer.
A model is "open weights". What do you surely get?
You can download it and run it on hardware that can handle it, within what its license allows.
The label does not guarantee they are published. Open weights is the trained model, not the recipe.
The license decides that, and some ban uses or limit large companies. Read it before using it in something you charge for.
Training a model is like baking a cake: the data are the ingredients, the training code is the recipe and computing is the oven. The weights are the finished cake. With open weights you get the cake: you can serve it, slice it and decorate it. But if you only get the cake, you do not have the recipe to bake an identical one.
The opposite is a closed model: its weights are not available for you to download. You use it through the app or the API of whoever built it, or of authorized providers.
In software, "open source" means you can use, study, modify and share the program. With AI, many people call any downloadable model "open source", but publishing the weights is not enough: the license, the code and information about the training data matter too. That is why "open weights" is used: it says exactly what you get.
Run it as a local model on hardware that can handle it: it can work offline and your data can stay there, if the app does not send it out. Compress it so it fits in less memory. Adjust it with your own examples (fine-tuning) so it sounds like your company. Or host it on your own server and stop depending on a provider changing the price, modifying it without notice or shutting it down.
Well known families such as Llama, Mistral, Qwen or Gemma publish weights. Being open does not force you to run it yourself: many providers also offer them through an API.
Free to download does not mean free of conditions. Some licenses are very broad and allow almost anything, even selling it inside your product. Others ban certain uses, require you to credit the model or set limits for large companies. Before you put it in something you will charge for, read the license of that specific model.
"Open weights is open source." The weights alone are not enough: you still need to look at the license, the code and the data. "If it is open, it fits on my laptop." It depends on the size: some open models need several graphics cards. "Open is worse than closed." Some open models compete with closed ones on many tasks; compare them on your own cases, not by the label.