Most of these confusable pairs are two different things people mix up. This one isn’t. Weights and parameters overlap almost entirely, which is exactly why the words get used interchangeably and why that mostly works until it doesn’t.
The useful distinction isn’t technical. It’s about what each word is doing in the sentence you’re reading.
Weights
Weights are the individual numbers a model learned during training. Each one sets how strongly one part of the network pulls on another. Nudge one, and the model’s behavior shifts a little. Nudge billions of them over months of training, and you get something that can write. Nobody can point at a specific weight and tell you what it’s for, which is a whole separate problem.
In practice, though, “the weights” usually refers to the whole file. When a company releases a model you can download and run yourself, what you’re downloading is the weights: a very large collection of numbers with no code, no interface, nothing else. That’s the artifact. It’s why the phrase is open weights and not open parameters.
Parameters
Parameters means every learned number in the model, weights included. There are a few other kinds in there (biases, mostly, which shift a value up or down rather than scaling it), so parameters is the wider category and weights is the bulk of it.
But you’ll almost never hear parameters used that way in the wild. It’s a count. Seven billion parameters, seventy billion, four hundred and five billion. It’s the number on the box, the one that goes in the launch post, and the rough proxy people use for how big and how expensive a model is. It’s a worse proxy than it used to be, since a well-trained small model routinely beats a lazily trained big one.
The tell
Listen for whether the word comes with a number or a verb.
If someone says a figure, they mean parameters. It’s a size. If someone says they downloaded it, ran it locally, fine-tuned it, or leaked it, they mean weights. It’s a file.
You can be sloppy about this in most conversations and nobody will stop you. The place it matters is when a company says its model is open. Open weights means you get the file. It doesn’t mean you get the training data, the code, or any say in what happens next.