I've found that current models will almost automatically sketch out some things in Python (or another suitable language for the type of task, or an implementation language you've already stipulated) while proposing a design, and you can go through a conversation of "what if we did xyz instead?" and at some point "okay, let's try writing a full prototype" (perhaps tacking on a bunch of decisions here so that things are resolved enough to work with).
But that's at the scale of <1kloc. Might be different if you're trying to do a bigger feature all at once.
But that's at the scale of <1kloc. Might be different if you're trying to do a bigger feature all at once.