>An LLM rewriting a codebase from scratch is only as good as the spec. If “all observable behaviors” are fair game, the LLM is not going to know which of those behaviors are important.

I've been using LLMs to write docs and specs and they are very very good at it.

That’s a fair point — I agree that LLMs do a good job predicting the documentation that might accompany some code. I feel relieved when I can rely on the LLM to write docs that I only need to edit and review.

But I’m using LLMs regularly and I feel pretty effectively — including Opus 4.5 — and these “they can rewrite your entire codebase” assertions just seem crazy incongruous with my lived experience guiding LLMs to write even individual features bug-free.