Open-Weight Models in Plain English

A model is a large file of numbers, called weights, that holds what training taught it. Most well-known chat assistants keep those weights private. You can use the model through their service, but you cannot download it.

An open-weight model is one whose weights are published so anyone can download and run them. You will also see the phrase open source, and the two are often used loosely as if they meant the same thing. Strictly, open source also means the training data and code are available, and many so-called open models only publish the weights and a licence. The licence matters, because it tells you what you may do with the model, including whether you can use it in a business.

Open-weight models come in sizes, measured in billions of parameters. Smaller ones are quicker and fit on ordinary computers but handle less complex work. Larger ones are more capable and need more memory.

Names and rankings change constantly, with new releases every few weeks, so instead of memorizing model names, learn to read the size, the licence and what it was built for.

Takeaway: open-weight models can be downloaded and run by anyone. Check the size and the licence, and ignore any list of names that claims to be permanent.

Tools, prices and features in this area change quickly. Last reviewed September 2026.