MODELS
Open Weights
Definition
AI models whose trained parameters are publicly downloadable, so anyone can self-host and fine-tune them even without the training data or code.In-Depth Explanation
"Open weights" is narrower than "open source." Releasing weights means you can download, run, and adapt a model, but the training data, code, and full pipeline are often withheld — so the model is not necessarily open source in the legal sense. Access falls on a spectrum: closed-api (hosted only, like GPT or Claude), open-weights-restricted (downloadable under a non-commercial or gated license), and fully-open (permissive Apache-2.0/MIT with weights, code, and data). Most models marketed as "open source" are really open-weight.
Real-World Example
Meta's Llama models are open-weight — downloadable from Hugging Face — but ship under a community license rather than a fully open one.
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