You do need to pair it with an account to activate basic skills, but:
> By default, Mycroft will not store your usage data or keep any recordings of your voice
https://mycroft-ai.gitbook.io/docs/using-mycroft-ai/pairing-...
"It is a bit of a chicken-and-the-egg situation, but I don’t think there is a strong case for creating an easy offline setup before the core components are ready. It is close, but I suspect it will be at least another year before we (the open source community) have all those pieces ready."
However, their backend seems to be on GitHub.