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Muse Spark Open: Meta releases an 816B open-weight model
816B total, 42B active, 1M context, weights under the Muse Model License.
Meta released the weights for Muse Spark Open on October 15, 2026. It is an open-weight sparse mixture-of-experts model with 816B total and 42B active parameters and a 1M-token context. Meta says it is built for coding and agent work.
What changed
- Weights are on Hugging Face in two checkpoints:
meta-models/Muse-Spark-Open-816B-A42B(BF16) andmeta-models/Muse-Spark-Open-816B-A42B-NVFP4. - The license is the Muse Model License, which Meta describes as having limited commercial terms. Hugging Face downloads need an access request.
- Input is text, image, video and audio. Output is text.
- vLLM shipped day-0 support, with prebuilt images for Nvidia and AMD.
- Meta names Baseten, Fireworks AI, Groq, Modal, Nebius, OpenRouter and Together AI as API partners.
Checkpoint sizes
Meta's figures for the weight files alone, before KV cache and runtime overhead:
| Checkpoint | Weight footprint |
|---|---|
| BF16 | About 1.65 TB |
| NVFP4 | About 537 GB |
Pricing
OpenRouter lists Muse Spark Open at $1.25 input and $4.25 output per million tokens, with cache reads at $0.15.
RouterPlus lists it on 2 providers. Prices per million tokens, from the live catalog on October 31, 2026:
| Provider | Input | Cached input | Output |
|---|---|---|---|
| Nebius | $1.25 | $0.15 | $4.25 |
| Doubleword | $1.25 | $0.15 | $4.25 |
What to do
- On RouterPlus, the model ID is
meta/muse-spark-open, called with one API key athttps://api.routerplus.com/v1. Sign up at app.routerplus.com/login and call the API right away. - RouterPlus does not have a Muse Spark Open model page yet. Browse every model on the RouterPlus models page.