Muse Spark Open

• - 🏢 Meta's open-weight reasoning model for coding and agentic workflows.
• - 🧠 Sparse mixture-of-experts: 816B total, roughly 42B active per token.
• - 📏 One-million-token context window for whole-repository work.
• - 👁️ Native image understanding alongside text in a single checkpoint.
• - 🔧 Tool calling supported for agentic, multi-step developer loops.
• - 🆕 Open-weight counterpart to Meta's hosted Muse Spark line.
• - 🌐 Distributed on Hugging Face as a downloadable checkpoint.
• - 💬 Produces explicit reasoning before final answers.

Meta

Meta Platforms is an American multinational technology company headquartered in Menlo Park, California. Best known for operating Facebook, Instagram, WhatsApp, and Threads, Meta has become one of the most influential players in open-weight AI research through…

Muse Spark Open is Meta's open-weight reasoning model aimed at coding and agentic workflows, released in 2026 as the downloadable sibling to the hosted Muse Spark models served through Meta's Model API. Architecturally it is a sparse mixture-of-experts network with roughly 816 billion total parameters and about 42 billion active per token, combining text generation with native image understanding in a single checkpoint and supporting tool calling and a context window of one million tokens.

Within Meta's own open-weight line, the clearest step is scale and modality. Hugging Face's launch write-up notes that Muse Spark Open follows Muse Glimmer, a far smaller open release, by introducing the mixture-of-experts architecture "at a much larger scale." Compared with Meta's earlier dense, text-only open models such as Llama 3.3 70B, the smaller Llama 3.2 3B, and the community-tuned Hermes 3 Llama 3.1 405b, Spark Open adds native visual input, explicit reasoning traces, tool calling, and a context window orders of magnitude longer.

The design is agent-oriented rather than purely conversational: the model is intended to plan, call tools, read results and continue over long horizons, which is what the very long context and function-calling support are there to enable.

For hosted, closed-weight alternatives in the same family, see Muse Wonder for coding work and Muse Image for image generation and editing.