Meta releases Muse Spark Open, an 816 billion parameter open weight model it calls the most capable US open weight model to date
Today we’re releasing Muse Spark Open, the most capable US open-weight model to date. Built for coding and agentic work, it excels at long-horizon tasks, complex software engineering, and multi-step reasoning. Key Model Specs: → 816B total / 42B active parameters → 1M token context window → Natively multimodal across text, image, video, audio
Context
A frontier class model with downloadable weights from a US lab changes what developers and companies can run themselves, and Meta says it fits on two desktop Macs.
This is a first hand launch post from Meta's AI account, posted at 1:08 PM ET, so its view count is still early. The most capable claim and the benchmark table are Meta's own. The weights use Meta's own Muse Model License with limited commercial terms rather than a standard open source license.
Deep dive
On October 15, AI at Meta posted: Today we're releasing Muse Spark Open, the most capable US open weight model to date. It said the model is built for coding and agentic work and excels at long horizon tasks, complex software engineering and multi step reasoning, with 816 billion total and 42 billion active parameters, a 1 million token context window and native multimodal input across text, image, video and audio.
In follow up posts Meta said the model is optimized to run on two Apple M5 Ultra Mac Studios with the MLX framework, runs on engines such as SGLang, vLLM, TensorRT LLM, Transformers, llama.cpp and Unsloth, and is available through API platforms including Baseten, Fireworks AI, Groq, Modal, Nebius, OpenRouter and Together AI. Weights can be downloaded from Hugging Face, Amazon SageMaker AI, Google Cloud Model Garden and Microsoft Foundry Models.
Meta's blog says Apple's unified memory lets each Mac Studio's GPU use up to 512 GB, so two machines hold the whole model, and that it tested on device agentic work such as shipping iOS changes to the open source Mastodon client Ice Cubes. Meta's benchmark table shows Muse Spark Open leading on several agentic, reasoning and multimodal tests, while Kimi K3 or GLM 5.3 score higher on others such as Terminal Bench 2.1 and GDPval.
Meta says the model got additional safety post training because weights are open and met the release thresholds of its Superintelligence Scaling Framework, with a full evaluation report coming. Mark Zuckerberg posted that it runs great on the new Mac Studios thanks to work with Apple.
What to expect next
Watch independent benchmarks and community tests to see whether Muse Spark Open holds up against Chinese open weight models such as Kimi K3 and GLM 5.3 outside Meta's own table.
Also watch the terms of the Muse Model License for larger companies, how many developers actually run it on Mac Studios, and whether Meta publishes the promised full evaluation report.