I read licenses the way I read scopes of work: looking for the one line that changes the price later. Muse Spark Open’s license has two of those lines, and the internet is already getting both of them slightly wrong.
So here’s the plain version, from the license itself — the Muse Model License Meta published with the Muse Spark Open weights on October 15, 2026.
First, what the license gives you. It grants the model free of charge, and the list of rights is long: use it, copy it, modify it, fine-tune it, distill it, merge it, publish it, distribute it, sublicense it, and sell copies of it. That is a real grant. Most developers, including commercial ones, can build on this model for free.
Now the famous line: twenty million dollars. Read it carefully, because it does not say what the headlines say it says.
The clause does not trigger when a company gets big. It triggers when two things are true at the same time. One: you or your affiliates are in the business of giving third parties access to AI models as a product or service, through an API or something like one — the license calls that “Model as a Service.” Two: your whole group’s gross revenue passes twenty million dollars in some consecutive twelve-month stretch. If both are true, you have to notify Meta and sign a separate written agreement before you offer this model, or anything derived from it, through that service.
In plain terms: the line is not drawn around companies. It’s drawn around a kind of store. If you’re selling raw access to the model by the API call, and you’re doing it at real scale, Meta wants a signature. Everybody else keeps walking.
The license says so itself, in the same paragraph. The clause does not apply to internal use. It does not apply to research. It does not apply to any commercial activity that isn’t model-as-a-service. And it does not apply to using the model as a component that powers features of your own product. A fifty-million-dollar company running this model inside its own software owes Meta nothing under that clause. A company half its size reselling API access owes a phone call.
I run Tygart Media. We are nowhere near twenty million in revenue, and we are not in the business of selling anybody API access to anything. So the clause doesn’t bind us — on either prong. I’m building an open-source shared-brain system on Meta’s models for the hackathon: a book and a tool any small company can take, plug into a folder of its own files, and run. Nothing in that is a model-as-a-service. The twenty-million line is a fence around a field I’m not standing in.
What would change if I ever were? Two things would have to happen, not one. We’d have to start selling access to the model itself — our own hosted API that other people pay to call — and the whole company’s gross revenue would have to cross twenty million in a rolling twelve months. Then, before offering Muse Spark Open through that service, we’d notify Meta and sign their separate agreement. Growth alone never trips it. Reselling access alone, at small scale, doesn’t trip it either. It takes the store and the size together.
The second line is smaller, and it’s the one that actually applies to small builders: the credit. Any product or service that uses the open weights — or a derivative of them — has to prominently display the words “Built with Muse Spark Open.” In the interface, or in the documentation, or on the website, or in the settings menu. Exact words. No revenue threshold on this one. A one-person shop owes the same line as everyone else.
And “derivative” is defined broadly enough to deserve a second read. It covers any model created, trained, fine-tuned, distilled, or otherwise improved using the model — or using its outputs. Train a smaller model on what Spark Open wrote, and that smaller model is a derivative. The credit travels with it, and so does the usage policy. That’s not a trap; it’s just a term you should know before you distill anything.
One more clause worth knowing, because it settles a question every builder asks: Meta claims no ownership of outputs generated by the model. What it writes for you is not Meta’s property under this license. The words are yours to publish, sell, or give away.
Now the honest fine print about my own build, because this is where people will get sloppy. The license I’ve been quoting governs the downloadable open weights — the Software, in its words. My shared-brain build doesn’t ship those weights. It calls muse-spark-1.3 through Meta’s hosted API, which runs under Meta’s API terms, a different document. So the notice and the twenty-million clause don’t legally attach to my repo through this license at all. I’m putting the credit line in the README anyway, because the build stands on Meta’s models and saying so costs me nothing — but I’m labeling it as what it is: a credit I chose, not a term I tripped.
That’s the whole shape of it. Free to use, free to build on, free to sell what you build — with a credit line on anything built from the weights, a usage policy that travels with every copy, and one revenue clause aimed squarely at the people reselling the model itself at scale. For a small shop, this license is not a catch. It’s a receipt that says the big door is open, and the only door with a lock on it is the one where you become the store.
Read the license before you build. Then build.
— Will Tygart, Tygart Media
Built with Muse Spark Open — a credit we carry by choice for this build; see the license map for what the term itself requires and of whom.
Sources: Muse Model License (version: Muse Spark Open, October 15, 2026), published on Meta’s model repo: https://huggingface.co/meta-models/Muse-Spark-Open-816B-A42B — opening grant; §1 (license travels with copies); §2 (notice + Derivatives definition); §3 (Model as a Service / $20M); §4 (no ownership of outputs); Exhibit A (Usage Policy).