Not OP but I think they meant Zig isn't 1.0 and therefore could be considered "not ready for prod". I'm not claiming anything about Zig; I can only hope that the Bun folks have done their due diligence and ran it through fuzzing/ASAN/etc before making the 1.0 stamp of approval.
That's the point being addressed by the comment you are responding to.
also stability is more of a statement about api design than internals
That in itself is no good argument -- it surely has some bug, and if, say, zig changes in the meanwhile and it can no longer compile the previous code then it can be problematic from a maintenance POV.
With that said, it is probably fine to use for most ordinary apps, but I wouldn't yet build a bank infrastructure on top for example.
Sure, the instability of Zig may increase the maintenance costs for Jarred, to use updated versions of Zig. But this has no effect on the features that Bun provides. The risk that a change to Zig would be so consequential that they would actually prevent Jarred from continuing to work on Bun, or would otherwise force Jarred to fork Zig, that risk is so low as to be inconsequential.
(disclaimer: not associated with either bun or zig, the above are pure opinions)