Meta Releases Open-Weight Model Muse Spark Open, Focusing on Long-Context Coding and Agentic Work

Meta released the open weights for Muse Spark Open on October 15, 2026, announcing its immediate availability on platforms like Fireworks AI. The model is a Mixture-of-Experts (MoE) architecture with 816 billion total parameters and 42 billion active per token, featuring a 1 million token context window designed for long-horizon coding and coherent agentic workflows.

According to benchmark results published by Fireworks AI, Muse Spark Open demonstrates strong performance in specialized domains such as law and finance. On Vals AI’s Harvey Legal Agent Benchmark leaderboard, it ranked first among 75 models with a pass rate of 25.4%, nearly four times that of Claude Opus 5 (6.7%). On Rogo’s Big Finance Bench, it outperformed Claude Opus 5.5 at every difficulty level and narrowly edged out GPT-6 Astra on the hardest tasks. Additionally, its scores in clinical documentation tasks were comparable to leading closed-source models but at lower token prices.

Beyond cloud services, Meta highlighted the model's local deployment capabilities. In collaboration with Apple, Muse Spark Open was optimized to run on two Mac Studios equipped with M5 Ultra chips, leveraging unified memory architecture to support large model inference. This flexibility allows enterprises to deploy high-performance AI in private environments while meeting data residency and security compliance requirements.

While the vendor claims this is one of the most powerful US open-weight models to date, some performance data comes from vendor self-tests or specific partner evaluations. Developers can download the weights via Hugging Face or use them on cloud platforms such as Amazon SageMaker AI and Google Cloud Model Garden.