Meta Releases Muse Spark Open, an 816B-Parameter Open-Weight AI Model

Meta released Muse Spark Open on October 15, 2026, a new open-weight artificial intelligence model the company describes as "the most capable US open-weight model to date." The model is a natively multimodal mixture-of-experts system with 816 billion total parameters and 42 billion active parameters per token. It supports a context window of 1 million tokens and accepts text, images, video, and audio as input, producing text output.

Architecture and Capabilities

According to Meta, Muse Spark Open is built for coding and agentic work, excelling at "long-horizon tasks, complex software engineering, and multi-step reasoning." The model uses a mixture-of-experts architecture with 256 experts per layer, where 8 experts are selected for each token. This design allows the model to maintain high capacity while keeping inference costs lower than dense models of equivalent scale.

The model card, published through Hugging Face, details that Muse Spark Open includes a 1.8-billion-parameter Perception Encoder for visual input and a vocabulary of 202,048 tokens. Training data covers more than 100 languages. Meta states that the open-weight version includes additional safety post-training to address risks associated with public distribution.

Apple Silicon Integration

A key feature of the release is its optimization for Apple hardware. Meta says Muse Spark Open is the first model in its class to run on a desktop using two Apple M5 Ultra Mac Studios with the latest MLX framework. Apple’s unified memory architecture allows the M5 Ultra's integrated GPU to use up to 512 GB per Mac Studio, enabling two machines to hold the entire model in memory. Meta describes this setup as two Mac Studios behaving like "one supercomputer with a terabyte of unified memory."

Meta demonstrated agentic workflows running entirely on-device, including shipping real iOS changes to the open-source Mastodon client Ice Cubes and driving DaVinci Resolve to review footage frame by frame.

Distribution and Licensing

Muse Spark Open is available through seven hosted inference platforms: Baseten, Fireworks AI, Groq, Modal, Nebius, OpenRouter, and Together AI. Model weights are available for download on Amazon SageMaker AI, Google Cloud Model Garden, Hugging Face, and Microsoft Foundry Models. According to MarkTechPost, the weights ship in BF16 and NVFP4 formats.

The model is released under the Muse Model License, which includes limited commercial terms. MarkTechPost reports that products using the model must display "Built with Muse Spark Open," and Model-as-a-Service providers with revenue above $20 million in a 12-month period require a separate agreement with Meta. Internal use, research, and powering own product features are exempt from the revenue clause.

Benchmark Performance

Meta compares Muse Spark Open against other leading open-weight models, including Kimi K3, GLM 5.3, and Qwen3.8. According to Meta's evaluation, Muse Spark Open scores 89.2 on MCP-Atlas, ahead of Qwen3.8 (84.5) and GLM 5.3 (84.2). However, on Terminal-Bench 2.1, a coding benchmark, Muse Spark Open scores 76.4, trailing Kimi K3 (85.0), GLM 5.3 (83.9), and Qwen3.8 (82.0).

Why it matters

The release of Muse Spark Open marks a strategic shift for Meta, which has historically focused on open models but recently pushed to compete with closed models from OpenAI and Anthropic. By releasing a highly capable open-weight model, Meta aims to reclaim ground in the open-weight market, which has been dominated by Chinese labs such as Alibaba, Moonshot AI, and Z.ai. The integration with Apple hardware also signals a new partnership between the two tech giants, potentially lowering the barrier for developers to run frontier-scale models locally.

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Sources

• research.meta.ai: Introducing Muse Spark Open, The Most Capable US Open‑Weight Model to Date | Meta AI Research
• theguardian.com: Meta releases Muse Spark Open, a new ‘open-weight’ AI model | AI (artificial intelligence) | The Guardian
• tech-insider.org: Meta Muse Spark Open Debuts on 7 Clouds 2026
• finance.yahoo.com: Meta Releases Muse Spark Open With an Unlikely Assist From Apple: Why It Can Afford to Give It Away
• marktechpost.com: Meta Releases Muse Spark Open: 816B Open-Weight MoE With 1M Context - MarkTechPost
• shattered.io: Meta Muse Spark Open: 816B Params, $1.25/M Tokens

This article was drafted with AI assistance and checked against the sources above. Company claims are reported as claims. Cover image is AI-generated.