They say that they have too much demand so are stopping new subscriptions while they scale up: https://x.com/Kimi_Moonshot/status/2078855608565207130

> Over the past 48 hours, demand has pushed close to the limits of our current capacity. To protect the experience of existing subscribers, we're temporarily pausing new subscriptions and prioritizing compute for current members. Existing subscribed users are not affected.

> We're adding capacity as fast as we can and will reopen new subscription spots in batches.

That might even be a beneficial move, creating (well, actual, not artificial) scarcity works well to draw interest usually. Curious how this one plays out.