Meta opens the weights of Muse Spark Open
On 15 October 2026 Meta released the weights of Muse Spark Open, which it calls the most capable US open-weight model to date: a natively multimodal model with 816B total parameters (42B active) and a 1M-token context, built for coding and agentic work. The weights can be downloaded from Hugging Face and several cloud catalogues; the licence is Meta's own Muse Model License with "limited commercial terms".
Why it matters
One of the largest models whose weights can be downloaded reaches developers under a bespoke licence rather than a standard open one, and Meta shows it running on two desktop computers from Apple. "Most capable US" is Meta's own wording, and how open the licence is depends on its text, which was not read here.
What the announcement says. Muse Spark Open is a "natively multimodal" model with 816B total parameters (42B active) and a 1M-token context window, "built for coding and agentic work". It is available through APIs at Baseten, Fireworks AI, Groq, Modal, Nebius, OpenRouter and Together AI; the weights can be downloaded on Amazon SageMaker AI, Google Cloud Model Garden, Hugging Face and Microsoft Foundry Models. It runs on SGLang, vLLM, TensorRT-LLM, Hugging Face Transformers, Apple MLX, llama.cpp and Unsloth. Meta calls it the first model of its class to run on a desktop: on two Apple M5 Ultra Mac Studios with MLX (up to 512 GB of unified memory each, 1.2 TB/s). For the open weights it shipped Helion kernels for SGLang with kernel-level speedups of 1.03 to 3.95 times on NVIDIA and AMD GPUs and a 3% end-to-end speedup on AMD MI350. Safety and licence. By Meta's account the model has additional safety post-training because the weights are open, was evaluated under the Meta Superintelligence Scaling Framework and "met the thresholds our framework requires for release"; results are in the model card and a full evaluation report is "available soon". The weights are released under the Muse Model License "with limited commercial terms, which allow many developers to use the model for free". What the record does not claim. The benchmark charts on the page (images) were not read; the model card and the licence text were not opened, so the limits of the "limited commercial terms" are not stated here. "Most capable US open-weight model" and "first of its class on a desktop" are Meta's words about itself.