Meta released the weights of Muse Spark Open, an 816B-parameter open-weight MoE model

On October 15, 2026, Meta released the weights of Muse Spark Open, a natively multimodal mixture-of-experts model with 816B total and 42B active parameters and a 1M-token context, under the Muse Model License.

Archive entry: this covers an event from October 15, 2026, and we published it on November 8, 2026. The details come from sources dated at the time and may have changed since.

On October 15, 2026, Meta released the weights of Muse Spark Open, a natively multimodal mixture-of-experts (MoE) model with 816B total and 42B active parameters and a 1M-token context. Meta announced it on the Meta AI Research blog and called it the most capable US open-weight model to date.

What changed

Muse Spark Open was a mixture-of-experts model with 816B total and 42B active parameters, a 1M-token context and native multimodality.
The weights shipped in BF16 and NVFP4 and were available on SageMaker, Model Garden, Hugging Face and Foundry, as meta-models/Muse-Spark-Open-816B-A42B on Hugging Face.
Supported engines were SGLang, vLLM, TensorRT-LLM, Transformers, MLX, llama.cpp and Unsloth.
Hosted API partners were Baseten, Fireworks, Groq, Modal, Nebius, OpenRouter and Together.
Meta said the model ran on two Apple M5 Ultra Mac Studios with MLX, each with 512 GB of memory and 1.2 TB/s of bandwidth.
Helion kernels delivered speedups of 1.03 to 3.95x and a 3% end-to-end gain on MI350.

What it meant for people building with AI

The release put a frontier-scale open-weight model from a US lab within reach of high-end desktop hardware, since Meta said it ran on two Apple M5 Ultra Mac Studios. Hosted API partners and a long list of supported engines gave teams more than one way to run it, from hosted endpoints to engines such as vLLM, MLX and llama.cpp.

License and safety

Meta released the model under the Muse Model License, which carries limited commercial terms. Meta said Muse Spark Open received extra safety post-training and met the thresholds in its framework. A second source for these details is the Models page of Meta's developer docs.

Sources

Introducing Muse Spark Open, The Most Capable US Open-Weight Model to Date (Meta AI Research, October 15, 2026, official)
Models (Meta (dev.meta.ai docs), official)

Written with AI assistance, strictly from the sources listed above. Before it went live, automated checks verified its dates, sources and every language edition.