Mistral Goes Closed Source (twitter.com)

That's not their first "closed-source" model. "mistral-medium" was.

Depending on your definition, none of mistral's models are "open source", AFAIK they've given no information on what training data they used, how many tokens they trained it with, etc.

Now we see the reason for all the hype over Mistral for the last six months or so.