Meta releases Muse Spark Open, its most capable US open-weight model

Meta released Muse Spark Open on October 15, 2026, describing it as the most capable US open-weight model to date. The model has 816 billion total parameters with 42 billion active per token, a context window of 1 million tokens, and native multimodal input. Meta built it for coding and agentic work, including long, multi step tasks.

Meta worked with Apple to tune the model for local use on Mac hardware; running it locally takes about a terabyte of memory, with two 512 GB M5 Ultra Mac Studios presented as the desktop setup. The weights are free to download under a license allowing limited commercial use, and the model is also available through several hosted API platforms.

Sources: TechCrunch; MacRumors