Muse Spark Open: Meta's 816B Open-Weight Model for Agents

Muse Spark Open is Meta’s October 2026 open-weight release of an 816B-parameter mixture-of-experts multimodal model, with 42B active parameters per token, a 1M-token context window, and support for text, image, video, and audio inputs, designed for coding and long-horizon agentic workflows. Meta reports leading results among compared open-weight models on MCP-Atlas and JobBench for tool selection, while several competitors outperform it on terminal and repository-focused coding benchmarks such as Terminal-Bench, DeepSWE, and SWE-Atlas-QnA. The model is available in BF16, NVFP4, and smaller quantized formats across NVIDIA, AMD, Intel, and Apple hardware, with an MLX version capable of running on multiple high-memory Mac Studios, as well as hosted API and cloud catalog options. Its custom Muse Model License permits commercial use, modification, fine-tuning, redistribution, and distillation but requires prominent “Built with Muse Spark Open” attribution and imposes additional terms on large companies selling model API access. The material emphasizes that quantization, fine-tuning, prompting settings, tool-call handling, and safety modifications can alter behavior from Meta’s evaluated checkpoint, recommending regression tests for agent performance, jailbreak resistance, destructive-action approvals, parallel tool calls, and multimodal edge cases before deployment.

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