Meta
Meta opens Muse Spark weights, but large API hosts need a deal
Meta released Muse Spark Open weights, which it calls the most capable US open-weight model. Hosts above $20 million in revenue need a separate deal.
Meta released the weights of Muse Spark Open, a model it calls “the most capable US open-weight model to date.” Many developers can use it free under a license with one catch. A company that sells the model to others through an API must sign a separate agreement with Meta once its revenue passes $20 million.
Meta announced the release Oct. 15, 2026, in a post on the Meta AI Research blog. Weights are the trained numbers that make up a model. Publishing them lets others run the model on their own hardware. That is “open weights.” Muse Spark launched as a closed model April 8, 2026, Axios reported.
The Model Is Large but Uses a Fraction of Itself at a Time
Muse Spark Open has 816B total parameters. Only 42B are active. That is how many it uses to process each token, a small chunk of text. It is natively multimodal and has a 1M-token context window, the amount of text it can read at once. Meta built it for coding and agentic work such as long tasks and multi-step reasoning.
It shares a base model with Muse Spark 1.3, according to a PyTorch blog post by the PyTorch Team at Meta. Extra safety training prepares it for standalone use without system guardrails. The full evaluation report will be “available soon,” Meta said.
The License Is Free Until a Company Resells the Model
Meta describes the Muse Model License as having “limited commercial terms, which allow many developers to use the model for free.” The Hugging Face model page is gated. Users accept the terms before downloading.
Products or documentation that use the model or its derivatives must display “Built with Muse Spark Open.” A company that provides AI models to third parties through an API must notify Meta and sign a separate written agreement before offering the model or derivatives. The license calls that “Model as a Service.” The requirement applies when aggregate gross revenue tops $20 million in any 12-month period.
Internal use, research and use as a component of a company’s own product are exempt.
Seven Hosts Offered API Access at Launch
Baseten, Fireworks AI, Groq, Modal, Nebius, OpenRouter and Together AI offered hosted API access Oct. 15.
OpenRouter’s model list, checked Oct. 16, 2026, shows a 1,048,576-token context, $1.25 per million input tokens and $4.25 per million output tokens. Prices get cut.
Meta Says Two Mac Studios Can Run It
Meta said Muse Spark Open is the first model in its class to run on a desktop. The setup is two Apple M5 Ultra Mac Studios with the latest MLX framework. Each M5 Ultra can use up to 512 GB of unified memory. The pair holds about a terabyte.
Our View
A host above $20 million in revenue has to notify Meta and sign a separate agreement before it offers Muse Spark Open or derivatives. A host below that line does not.
Developers who buy the model through an API can ask a host which side of the line it is on. The answer shows whether the host’s access rests on terms between that host and Meta.
Developers building the model into their own products are exempt. Research is exempt too. Running the weights on one’s own hardware is not Model as a Service. Meta’s two-Mac setup uses about a terabyte of memory.
A host’s right to offer the model without a separate Meta agreement holds only while its revenue stays under $20 million.