Meta has released Muse Spark Open, an 816-billion-parameter model whose weights can be downloaded and run outside Meta’s services. It activates 42 billion parameters per token and supports a million-token context window. The release arrived on 15 October, three days after Muse Wonder and Wonder Full. 1
The model accepts text, images, video and audio, and produces text. Meta is pitching it for coding and agents that have to work through several steps, with reasoning effort adjustable from low to xhigh. Its published comparisons use xhigh. 2
The strongest results are in tool use
In Meta’s launch table, Spark Open scores 89.2 on MCP-Atlas and 61.8 on JobBench, ahead of the other models listed on both tests. Its 26.1 on HLE-Diamond without tools also leads that comparison. On the visual side, it reaches 50.0 on ZeroBench and 73.6 on SimpleVQA with tools.
The table is less flattering on coding. Spark Open’s 76.4 on Terminal-Bench 2.1 trails Kimi K3 at 85.0 and GLM 5.3 at 83.9. Its 1,401 on GDPval-AA v2 also falls behind several competitors. There are clear strengths here, but the results do not establish an across-the-board lead.
Downloadable, with substantial hardware requirements
Meta says the model can run across two M5 Ultra Mac Studios using MLX. Hosted access is also being offered through inference partners including Fireworks AI, Together AI and OpenRouter. That gives developers a way to try it without first assembling a local setup.
The model card lists BF16 and NVFP4 weights, with GPU memory requirements of at least 2TB and 700GB respectively. The 42B active-parameter figure describes how much of the model is used per token; it does not make the full 816B model small enough for an ordinary consumer GPU.
What “open” allows
The weights come under the Muse Model License, which permits modification and redistribution but carries conditions. Products using the model must display the required attribution. Model-as-a-service providers whose own and affiliated businesses exceed $20 million in aggregate gross revenue over a consecutive 12-month period must notify Meta and obtain a separate agreement before offering it or derivatives in that business. The clause excludes internal use and products that are not model-as-a-service. 2
Sources & references
- Meta: Introducing Muse Spark Open ↗
15 October 2026. Release, distribution partners and local deployment demonstrations.
- Meta: Muse Spark Open model card and licence ↗
Architecture, modalities, memory requirements, evaluation settings and Muse Model License. Read on 15 October 2026.
