Muse Spark Open: Meta opens the weights, and it runs on two Mac Studios
Meta has opened the weights of Muse Spark Open, an 816-billion-parameter multimodal model that Apple and Meta made runnable on two M5 Ultra Mac Studios. For developers, it's a model you can host yourself, provided you're ready to pay for the hardware.
Open weights, after a long detour through closed doors
On 16 October 2026, Meta opens the weights of Muse Spark Open, which it calls “the most capable open-weight model in the United States.” It is a multimodal model with 816 billion parameters, of which 42 billion are active for each token thanks to a Mixture of Experts architecture, and it has a context window of one million tokens. It takes text, images, video and audio as input, but it only generates text.
Meta’s road back to open weights was not a straight one. Llama 4, released in April 2025, was dogged by accusations of benchmark manipulation, and Muse Spark, the first model from Meta’s new lab, was closed. The return to open weights went through Muse Glimmer, a 30-billion-parameter model released under an Apache 2.0 licence.
Solid numbers, but not on every table
Meta bills Spark Open as “built for coding and agentic tasks.” On agentic tasks, it tops two of the three benchmarks against competing open models, JobBench and MCP-Atlas. On GDPval-AA v2, it is beaten by three Chinese models and by Mistral Large 4.
Coding is less flattering: it trails four rivals on Terminal-Bench 2.1 and sits mid-pack on DeepSWE. Across eleven benchmarks, Meta claims six first places, but the table does not pit the model against the closed offerings from OpenAI and Anthropic. A score published by the vendor is still the vendor’s score, so check it on your own tasks before you trust it.
Two Mac Studios and a terabyte of memory
The model runs on the integrated GPU of Apple’s chips, using their unified memory and a bandwidth that reaches 1.2 TB/s. A 4-bit quantised version of the 816 billion parameters stays in memory when split across two Mac Studios with 512 GB each, one terabyte in total. The sharing runs through MLX, Apple’s framework, over Thunderbolt 5 links. Meta says you can scale up to four Mac Studios.
The price has not been announced. Next estimates that a setup of two M5 Ultra Mac Studios would easily exceed 30,000 euros, since Apple has not yet set the price of the 512 GB option. That is one outlet’s estimate, so treat it as exactly that.
What it means for you as a developer
In practical terms, an open-weight model downloads and runs on your own hardware. Your code and data never have to leave the machine, which matters if you work on confidential code. The million-token window lets you load large repositories, and the output is still just text. The article does not specify the licence for Spark Open. Muse Glimmer, the smaller sibling, is Apache 2.0, but that tells you nothing about the biggest model. Read the terms before you adopt it, not just the press release.
So the dream of a model of your own is within reach. You just need a desk big enough to hold the hardware and a bank balance with plenty of patience.
Sources (1)
Written with AI assistance from the sources cited above, then reviewed and approved before publication by Sébastien Soulier.
