I think this makes two incorrect assumptions:

1. That a human, even a brilliant human with a lot of experience, can sit down and one-shot a language spec for a new language that is actually good.

2. That an agent can produce code that is good enough for a programming language that intends to last for decades without exhaustive human review.

We might advance to the point where 2 is true, we're not there yet. We'll never make a better human that can one-shot a good programming language. It takes iteration, with a human in the loop. Zig has taken ten years to get to this point, and is still occasionally experiencing major refactors.

If you want to argue an LLM could potentially accelerate development by some amount, I would agree with you. How much it could accelerate it is debatable. And, I understand why the Zig folks have decided not to accelerate in that way. There is a cost to it. You lose the junior programmer pipeline, as your "good first bug" list gets chewed up by people using LLMs. You still have to exhaustively review the code for a critical path like a compiler and AI code is hard to review; it doesn't have a point to it. The model doesn't want anything, so it's not always clear where it's going. Code without clear intention, like prose without clear intention, is hard to read and hard to review. It's verbose and often makes weird assumptions.

If I, for some reason, needed to implement a tiny DSL for something, I would 100% do it with an LLM. If I, for some reason, were tasked with building the best programming language to replace C, I would not hand it to an LLM (though I would get help from an LLM, because I don't know how to build a programming language beyond the tiniest toy interpreter or compiler, I'd need to read and understand every line of code, and use it daily, for it to turn out good).

For complicated problems, you can't just write the language spec. You need to iteratively develop it, which itself requires some intermediate state/language describing what you know so far. That intermediate state being the end programming language in consideration isn't mandatory per se, but iteratively refining, replacing, and reworking solutions using code as a drafting board is very common in the industry. That's doubly true for languages, where the social pressures in how it "feels" or is actually used are paramount. If you move away from iterative coding drafts, you still need some sort of interactive product to work on to actually develop the spec.

Plus, current-gen agents/LLMs can't implement a non-trivial language spec without significant hand-holding.

I’ve been thinking about this over the past few days. There was an exciting keynote at PLDI 2026 by MIT professor Saman Amarasinghe where he talked about the intersection between compilers and machine learning, including LLMs. One of the works discussed during the keynote was the use of Claude Code by his colleague Martin Rinard to implement a compiler known as a credible compiler that outputs both compiled code and a proof that the output code correctly matches the input.

https://youtu.be/Fc3cW0nqAQ0

Such a spec would never survive contact with reality. Maybe a human could stumble their way through iterating on it with the help of an LLM, but with current models you’re going to end up with nothing but a steaming pile of garbage. Not Zig.