Meta releases Muse Spark Open, an 816B open-weight model that runs on two Mac Studios

Meta on Thursday, Oct. 15, 2026, released the weights for Muse Spark Open, a natively multimodal model with 816 billion total parameters (42 billion active) and a 1-million-token context window that it calls the most capable US open-weight model to date, and said it worked with Apple so the model can run on a desktop pair of M5 Ultra Mac Studios.

The biggest US open-weight model yet now fits on a desk — if your desk holds two top-spec Mac Studios. That is a real shift in where frontier-class agents can run: no cloud bill, no data leaving the building. It also puts Apple silicon in a spot Nvidia usually owns, and it makes Meta and Apple allies after years of sniping. Open weights under a limited license are still a gift with strings, but the strings got a lot longer.

Meta released the weights for Muse Spark Open on Oct. 15, 2026. Open-weight means the learned numbers are downloadable so someone else can run the model. Meta calls it the most capable US open-weight model to date. Those lines are Meta's. The license is not open source. It is the Muse Model License, with limited commercial terms that Meta says let many developers use it for free.

The model is natively multimodal: it is built to take more than one kind of input, such as text and images, rather than text alone. Meta says it has 816 billion total parameters and 42 billion active. CNBC describes that split as a mixture of experts, meaning only a slice of the model runs for each piece of text. The context window is 1 million tokens. A token is a chunk of text, often a word or part of a word. Meta says it built the model for coding and agentic work, long-horizon tasks, complex software engineering, and multi-step reasoning. An agent, here, is software that can take a chain of steps, not only answer a chat. Those figures and claims are Meta's, except the mixture-of-experts line, which is CNBC's.

Meta says Muse Spark Open is the first model in its class to run on a desktop, using two Apple M5 Ultra Mac Studios and Apple's latest MLX software. MLX is Apple's toolkit for running this kind of model on a Mac. Meta says the M5 Ultra GPU can use up to 512 GB of unified memory per Mac Studio, so two machines can hold the entire model, and that memory bandwidth is 1.2 TB/s. Those lines are Meta's.

CNBC reports that customers can pair two to four Mac Studios to code, analyze video, or do other agentic work, and that Apple published new chip benchmarks and MLX technical documentation about splitting open models across machines. Mark Zuckerberg wrote on X: "Muse Spark Open -- weights releasing today -- runs great on new Mac Studios thanks to work with @johnternus and Apple." Apple CEO John Ternus replied congratulating the team. Meta AI chief Alexandr Wang said: "We worked with Apple to bring leading Agent capabilities to your desktop for the first time on the Apple M5 Ultra Mac Studios." Apple and Meta declined to say whether this is the start of a deeper relationship. Those lines are CNBC's, except the Zuckerberg and Wang quotations, which are theirs as CNBC prints them.

Meta's on-device tests used Muse Code powered by Muse Spark Open. Meta says the setup shipped real iOS changes to Ice Cubes, an open-source Mastodon client: bug fixes, new features, and a full build. It also says the model drove DaVinci Resolve end to end, reviewing footage frame by frame and cropping vertical clips. Those demonstrations are Meta's.

Hosted API partners, as Meta lists them: Baseten, Fireworks AI, Groq, Modal, Nebius, OpenRouter, and Together AI. Weights are downloadable on Amazon SageMaker AI, Google Cloud Model Garden, Hugging Face, and Microsoft Foundry Models. Meta also lists serving engines, chip optimizations, and Helion GPU kernel speedups in Sources.

On safety, Meta says it did additional safety post-training for the open weights, evaluated the model under its Superintelligence Scaling Framework, and met its release thresholds. Results are in the model card. A full evaluation report is "available soon." Those lines are Meta's. The full report is not out.

The picture is Meta's official release graphic. It reads Muse Spark Open Weights, with a line calling the model the most capable US open-weight model to date, over blue flowing lines. It is the company's social image for the post. The frame does not print a calendar date.

In plain terms, Meta said on Thursday that Muse Spark Open's weights are out: 816 billion total parameters, 42 billion active, a 1-million-token window, and a claim that it is the strongest US open-weight model yet. Meta and Apple tuned it to run on two M5 Ultra Mac Studios. You can download the weights or call a hosted API. The license is limited commercial, not open source. Meta's full safety report is still "coming soon."