Muse Spark Open

Muse Spark Open is Meta's open-weight release of the Muse Spark model family, announced October 15, 2026. It is a mixture-of-experts model with 816 billion total parameters (42 billion active per token), a 1-million-token context window, and native multimodal input: text, image, audio, and video in, text out. Meta describes it as the most capable US open-weight model to date, a claim based on the company's own evaluation table.

The weights were downloadable from day one in BF16 and NVFP4 formats across Hugging Face, Amazon SageMaker AI, Google Cloud Model Garden, and Microsoft Foundry Models. Meta demonstrated the model running on two M5 Ultra Mac Studios with 512GB of unified memory each through Apple's MLX framework; the model card lists at least 700GB of accelerator memory for the NVFP4 build. Day-one serving support covers vLLM, SGLang, TensorRT-LLM, Transformers, MLX, llama.cpp, and Unsloth, and seven hosted API providers serve it, including Together AI, Fireworks AI, Groq, Baseten, Modal, Nebius, and OpenRouter.

The model ships under the Muse Model License: free for most commercial use including fine-tuning, distillation, and redistribution, with products required to carry a "Built with Muse Spark Open" attribution. Businesses whose model-serving revenue exceeds $20 million in any consecutive 12 months must sign a separate agreement with Meta; internal deployment and research are exempt.