Meta has published the weights for Muse Spark Open, a coding and agent model the company says is less advanced than the Muse Wonder frontier model it launched on Monday. Chief AI officer Alexandr Wang stated that Meta will generally not open-source its most powerful models — the same distinction that the EU AI Act’s open-source exemption is built around.

Bloomberg reported the release on Thursday. Muse Spark Open is built for coding and agents, and Meta says it is less capable than Muse Wonder.

“Because of both safety and capabilities, we will generally not open-source our most powerful models,” Wang said, while adding that Meta intends to keep releasing capable open models.

Availability and Infrastructure

The weights are hosted on Hugging Face, Amazon SageMaker AI, and Google Cloud Model Garden. Nebius, the Dutch firm Meta has committed up to $27 billion to, is among the platforms serving the model.

The Muse Open-Weight Lineage

This is the second open release from the Muse line. Meta published Glimmer in August, a 30-billion-parameter model distilled from Muse Spark, under the Apache 2.0 licence. Meta also worked with Apple to ensure the new model runs on two M5 Ultra Mac Studios.

Meta said on Monday that Muse Wonder had reached the frontier but published no benchmarks. That model remains closed. In September, the company had not decided whether to publish the weights for Muse Spark 1.3, and has responded with a different model instead.

EU AI Act Implications

Article 53 of the EU AI Act exempts genuinely free and open models from documentation requirements owed to the AI Office. That exemption ends at systemic risk, where every obligation applies regardless of licence.

The Commission can fine companies 3% of global turnover and demand evaluations before release. Meta declined to sign the code of practice written to operationalise those duties, and Joel Kaplan said last year that Europe was on the wrong path.

Meta’s position also marks a shift in tone from its founder. Five weeks ago, Mark Zuckerberg told the Sources podcast that rivals training more advanced models and then withholding them was quite dangerous, though he named no company.

Open Source as a Geopolitical Argument

Wang said most of the world’s AI will run on open models and argued they should be American. Eight days earlier, Alibaba chairman Joe Tsai told a Turin conference that open source was Europe’s only path to technological independence. Wang expects Chinese developers to build on Muse Spark Open, and suggested it might even be beneficial if they adopted its underlying principles.

Europe’s own response is already in the market. Mistral launched Large 4, a trillion-parameter open-weight model, positioning it to compete with China’s growing lead in the open-weight category.