Meta releases Muse Spark Open, an 816B open-weight model under the Muse Model License

What Meta released

Meta published the weights of Muse Spark Open on 15 October 2026. In its announcement, Meta calls it the most capable US open-weight model to date and says it is built for coding and agentic work. The model card on Hugging Face describes a mixture-of-experts Transformer with 816B total and 42B active parameters, 256 experts with 8 active per token, and a 1.8B-parameter perception encoder. It takes text, image, video and audio input, outputs text, and supports a 1M-token context at inference.

The weights come in BF16 and NVFP4. The card says self-hosting needs at least 700GB of VRAM for NVFP4 and 2TB for BF16, while Meta's developer post gives about 530 GB for NVFP4, served on four Blackwell Ultra GPUs or eight H200s. Meta also says the model runs on two Mac Studio machines with M5 Ultra chips using MLX.

What the Muse Model License allows

The license text on the model card lets licensees use, copy, modify, fine-tune, distill, merge, publish, distribute, sublicense and sell the model and its derivatives. Section 2 requires a prominent "Built with Muse Spark Open" notice in the product interface, documentation, website or settings menu. Section 3 applies to Model as a Service: if a licensee gives third parties API access to model outputs and its group's gross revenue exceeds $20 million in any 12-month period, it must notify Meta and sign a separate written agreement before offering the model or its derivatives in that business.

Section 3 does not apply to internal use, research, commercial activity that is not Model as a Service, or use of the model to power features of the licensee's own product. Meta claims no ownership of outputs. An attached Usage Policy bans uses such as malware, impersonation and weapons work, and the card says the model is not intended for people under 18. Hugging Face lists the repository as gated, so downloads require approved access.

What changed for developers

Meta's smaller Muse Glimmer 30B is tagged Apache 2.0 on Hugging Face. The larger model instead carries attribution and a revenue-linked hosting rule. In practice, most companies that build the model into their own apps are outside Section 3, while large inference providers reselling API access must negotiate with Meta. Meta lists Baseten, Fireworks AI, Groq, Modal, Nebius, OpenRouter and Together AI as hosted API partners, but the terms of those agreements are not stated. On the card's benchmarks at the highest reasoning setting, Meta reports 89.0 on GPQA Diamond, 76.4 on Terminal-Bench 2.1 and 80.4 on OSWorld Verified.

What to watch next

Meta says a full evaluation report will follow, and the date is not stated. Watch for how inference providers above the revenue threshold describe their agreements with Meta, and whether the same license is used for later Muse releases. For comparison, Alibaba put Qwen-Image-2.1 under a non-commercial license in September. The release is listed on the AI model release tracker, and other license changes are collected under Open Source AI.

Questions people ask

Is Muse Spark Open open source?

Meta releases the weights, but under its own Muse Model License rather than an OSI-approved license. It allows commercial use and modification, with an attribution notice and a separate agreement for large Model as a Service businesses.

Who needs a separate agreement with Meta to use Muse Spark Open?

A licensee that offers the model to third parties as a service through an API, where its group's gross revenue exceeds $20 million in any 12-month period. Internal use, research and features inside its own product are excluded.

What hardware does Muse Spark Open need?

The model card says at least 700GB of VRAM for NVFP4 and 2TB for BF16. Meta also says it can run on two Mac Studio machines with M5 Ultra chips using MLX.

Sources

1. Introducing Muse Spark Open, The Most Capable US Open-Weight Model to Date (Meta, 15 Oct 2026)
2. Muse-Spark-Open-816B-A42B model card and Muse Model License (Meta on Hugging Face, 15 Oct 2026)
3. Build with Muse Spark Open (Meta, 15 Oct 2026)
4. Muse-Glimmer-30B model card (Meta on Hugging Face, 9 Aug 2026)