The multimodal model has 816bn total parameters, with 42bn active parameters and a 1m-token context window.

Meta has unveiled Muse Spark Open, calling it the “most capable” US open-weight model to date. The company said that the new model is the first in its class to be able to run on a desktop computer using two of Apple’s M5 Ultra Mac Studios with its latest machine learning framework.

The multimodal model has 816bn total parameters, with 42bn active parameters and a 1m-token context window. According to the company, it is built for coding, agentic work and other complex, multi-step reasoning tasks.

Unlike their closed-weight contemporaries, developers can download parameters of an open-weight model and modify them for their needs. Open-weight models, however, are not the same as open-source models that also provide access to training data and code.

Meta said that the model weights are available for download via Amazon SageMaker AI, Google Cloud Model Garden, Hugging Face and Microsoft Foundry Models. The model is available through popular API platforms including Groq, OpenRouter and Baseten.

China currently leads the open-weights space, with models developed by Chinese makers such as Xiaomi, Z AI, Kimi, Alibaba and DeepSeek routinely ranking above their US counterparts in Artificial Analysis’ ranking.

Muse Spark Open has had additional post-training safety, the company said. It evaluated the model across its “most severe risks” and found that it met the thresholds set by Meta.

Open-weight models are considered necessary for AI leadership, as being able to tweak a model means organisations, from start-ups to public institutions, can build on advanced models without training one from scratch.

Earlier this month, France’s AI darling Mistral announced its latest open-weight AI model Mistral Large 4, which it said “significantly outperforms” any open-weight model developed in the US or Europe.

Known as ‘Le Chonk’, ML4 is a 1trn-parameter natively multimodal model with 49bn active parameters, and Mistral’s “largest and most capable model to date”.

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