Meta has released Muse Spark Open — a new open-weight AI model built for desktop agentic work, and says it runs best on Apple’s Mac Studio with M5 Ultra chip. The model is available now on Hugging Face, with Meta explicitly positioning it as the “most capable US open-weight model to date.” It’s not a phone chip, not a cloud API, and not a mobile app: this is a 816B-parameter multimodal model designed to run locally, end-to-end, on high-end Apple silicon desktops. And it’s optimized using Apple’s MLX framework. An open-source array library built for unified memory architecture, which Apple itself just spotlighted in a fresh research post on its Machine Learning site.  Muse Spark Open uses only 42B parameters actively per inference, but its 1M-token context window and native multimodality let it handle long-horizon coding tasks, full iOS app builds, and even frame-by-frame video analysis inside DaVinci Resolve, all without touching the cloud.  Two Mac Studios with M5 Ultra chips can pool up to 1TB of unified memory, thanks to the chip’s 1.2 TB/s bandwidth and support for up to 512 GB per unit. That lets them jointly host and run the full model. A setup Meta calls “a supercomputer on your desk.”  The collaboration is unexpected. Apple and Meta have had a publicly frosty relationship for years. But according to Meta AI chief Alexandr Wang, quoted by Axios, the two companies have been working together “for several months.” Wang joked about the thaw, calling it “mommy and daddy playing nice again”. And credited former Apple executive Daniel Gross with helping bridge the gap.  This isn’t a consumer product launch. There’s no price, no app store listing, no prebuilt UI. It’s a developer release: weights on Hugging Face, documentation tied to MLX, and demos focused on real-world agentic workflows, like shipping live iOS code changes to Ice Cubes, an open-source Mastodon client.  What it means for users? If you own a Mac Studio with M5 Ultra. Or plan to buy one, Muse Spark Open is now the most powerful open model confirmed to run natively, privately, and fully on-device. No subscription. No telemetry. No internet required after download.  Apple hasn’t announced any hardware bundling, software integration, or retail promotion around Muse Spark Open. And Meta hasn’t said whether it plans to bring the model to other platforms. Though its reliance on MLX strongly implies Apple silicon remains the primary target for now.  The rollout is live. Developers can pull the weights from Hugging Face starting today.