Muse Spark Open
Meta · US · #4 in our ranking · Best US model
Muse Spark Open is an open-weight mixture-of-experts model from Meta (United States), released Oct 2026, with 816B parameters (42B active per token), a 1M-token context window, and the Muse Model License.
Muse Spark Open shares its base model with Muse Spark 1.3 and adds extra safety post-training so it can run without Meta's system guardrails. Meta calls it the most capable US open-weight model to date, with its best score on MCP-Atlas tool use.
Muse Spark Open specs
- Provider
- Meta
- Origin
- US
- Architecture
- Mixture-of-experts
- Parameters
- 816B total · 42B active
- Context
- 1M tokens | 786K words
- License
- Muse Model License
- Input
- Text, Image, Audio, Video
- Released
- Oct 2026
- Weights
- Hugging Face
Sourced from the model card on Hugging Face. Last checked 2026-10-16.
Highlights
- 816B total, 42B active
- Text, image, audio, and video input
- Runs on SGLang and vLLM
Where it fits for payment teams
A fit for teams whose vendor review asks for a US-built model, on agentic work like dispute packets or merchant reviews.
Harnesses in Runtime
Run Muse Spark Open through any of these harnesses on Runtime.
Provider-reported benchmarks
| MCP-Atlas | 89.2 |
|---|---|
| Terminal-Bench 2.1 | 76.4 |
| GPQA Diamond | 89.0 |
Benchmark scores are reported by each model provider on its Hugging Face model card. They are not independently verified by Runtime.
How to run Muse Spark Open
Download the weights
Pull meta-models/Muse-Spark-Open-816B-A42B from Hugging Face. Check the Muse Model License.
Serve it in your cloud
vLLM or SGLang on your GPUs, or a managed host.
Put it to work in Runtime
Point an agent or skill at it, then compare with evals.
Muse Spark Open FAQ
What is the context window of Muse Spark Open?
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Muse Spark Open supports a 1M-token context window (1,048,576 tokens), roughly 786K words of English text.
How many parameters does Muse Spark Open have?
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Muse Spark Open is a mixture-of-experts model with 816B total parameters, of which 42B are active per token.
Is Muse Spark Open free for commercial use?
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Muse Spark Open is released under the Muse Model License, a custom license. Commercial use may come with conditions, so read the license on Hugging Face before you deploy or fine-tune it.
What can Muse Spark Open take as input?
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Muse Spark Open accepts text, image, audio, video input and generates text.
Can I run Muse Spark Open in my own cloud with Runtime?
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Yes. Download the weights from Hugging Face (meta-models/Muse-Spark-Open-816B-A42B) and serve them with vLLM or SGLang in your cloud, or use a managed provider that hosts the model. Runtime agents can then use Muse Spark Open through a harness like OpenCode, with your data staying in your environment.