Meta releases open-weight Muse Glimmer model, keeps Muse Spark closed

Each sentence links inside to the piece that supports it.

People following Meta’s AI releases can see two different access levels at once: one Muse model is open weight, while another remained closed at the time of the earlier rollout. That matters today for developers and users who track what can be tested or built on, because the two models were not handled the same way.

In practice, public testing in Arena means Muse Spark Open moved into a setting where people could try it directly, while the open-weight release status stayed in place. The Arena step changes where the model can be examined, but it does not say that the model stopped being open weight.

The move was larger before the first headline than after. That is an observation, not an explanation: the market also moves on things nobody publishes.