Meta releases the open weights of Muse Spark Open, an 816-billion-parameter model it calls the most capable US open-weight model, though its own table puts it behind GLM 5.3 and Kimi K3

Meta released the weights of Muse Spark Open on 15 October. Its blog says: “Today, we’re releasing the weights for Muse Spark Open, the most capable US open-weight model to date.” It is a mixture-of-experts model with 816B total parameters (42B active) and a 1M-token context window, aimed at coding and agent work. The weights are on Hugging Face.

Meta says the model is available through API platforms at Baseten, Fireworks AI, Groq, Modal, Nebius, OpenRouter and Together AI, and it showed the model running on two Apple M5 Ultra Mac Studios.

The licence is new. The Hugging Face model card requires users to display “Built with Muse Spark Open”. If a licensee's gross revenue, with its affiliates, exceeds $20m in any 12 consecutive months, it must notify Meta and sign a separate written agreement before offering the model as a service.

Meta's own benchmark table does not put the model first. On the Artificial Analysis Intelligence Index it scores 39, against 45 for GLM 5.3 and 44 for Kimi K3, both Chinese open models. On Terminal-Bench 2.1 it scores 76.4, against 83.9 and 85.0. Those are Meta's figures, not an independent test.

Meta says it evaluated the model under its Meta Superintelligence Scaling Framework “and it met the thresholds our framework requires for release”, with a full evaluation report available soon. This is a separate model from Muse Wonder, the paid frontier model Meta released on 13 October.

• Claimed Meta calls Muse Spark Open “the most capable US open-weight model to date”, with 816B total parameters (42B active) and a 1M-token context window. Meta AI Research
• Confirmed The licence requires a separate written agreement with Meta before the model is offered as a service by a licensee whose group revenue exceeds $20m in any 12 consecutive months. Hugging Face model card
• Claimed Meta's table gives Muse Spark Open 39 on the AA Intelligence Index, against GLM 5.3's 45 and Kimi K3's 44. Hugging Face model card