Meta releases Muse Spark Open, an 816B-parameter open-weight model

Meta released the weights of Muse Spark Open on 15 October 2026 and calls it the most capable US open-weight model to date. It is a mixture-of-experts model, which uses only part of its network for each token: 42B of its 816B parameters are active at a time. It takes text, images, video and audio, answers in text and has a 1M-token context window. Meta built it for coding and agent work.

The weights, in BF16 and NVFP4 versions, are on Hugging Face, Amazon SageMaker AI, Google Cloud Model Garden and Microsoft Foundry Models. Seven providers, including Fireworks AI, Groq, OpenRouter and Together AI, serve it through an API, and Meta’s announcement gives no prices.

Meta’s model card says it needs at least 700GB of GPU memory in NVFP4 and 2TB in BF16. It also runs on two Mac Studios with M5 Ultra chips using Apple’s MLX framework, since each machine can give its GPU up to 512GB of memory.

In the scorecard Meta published, it leads 6 of 11 benchmarks against other open-weight models, and Kimi K3 leads 4.

The Muse Model License lets developers use, modify and sell products built on the model free of charge, if they show “Built with Muse Spark Open”. Companies that sell model access through an API and have more than $20 million in gross revenue over 12 months need a separate agreement with Meta first. Meta says the model met the release thresholds of its Meta Superintelligence Scaling Framework.