Meta Muse Spark Open in chat: 816B open weights, 1M context
Meta's Muse Spark Open is available in FastMetal chat. Meta released the weights on October 15, 2026. It is the first open-weight model in the Muse Spark line, and Meta calls it the most capable open-weight model from a US lab.
Muse Spark Open is a chat-only model on FastMetal: you use it in the web chat, and it is not available through the API or MCP.
What it is built for
- Coding and agentic work. Meta says it trained the model to read large codebases, plan a change, call tools, check the results and fix its own mistakes.
- An 816B mixture of experts with about 42B active parameters per token. The weights are on Hugging Face.
- A 1M-token context. We serve it with 1,048,576 tokens, enough for a whole repository or a long specification in one message.
- A reasoning model that reads images. It thinks before answering. Before launch we checked image input, tool calling and JSON-format answers on real requests.
Pricing
Muse Spark Open is billed per million input tokens and per million output tokens. Thinking tokens count as output. Current rates are on the model page.
Billing is prepaid: you load a balance by card, from $5, and you can never spend more than you loaded. See pricing.
How to use it
- Create a FastMetal account.
- Load a balance.
- Open chat and pick Muse Spark Open from the model list. Attach images to a message as you need them.
Compare real answers first
The model page shows Muse Spark Open's actual answers to our 43 shared prompts: summaries, bug fixes, translation and more. Compare them with Meta's Muse Spark 1.3 or with the model you use today. Everything we serve is in the model catalog.