?

https://github.com/ziglang/zig

Means not, thanks :)

Not only not any more, Zig has never been closed source.

Correct me if I'm wrong, but the code is there and licensed under MIT (Expat https://directory.fsf.org/wiki/License:Expat), which is GPL-compatible and "free". What's missing for it to be open source?

Edit: I might misunderstand your comment, ignore me if so.

you might've mistaken it for v which has been open-sourced in the meantime: https://github.com/vlang/v

Is it still full of impossible promises that strangely enough always get postponed or silently removed from the webpage?

Right, that's the one thank you :D