700k LoC of human written code is probably like 2M LoC of LLM "slop". That's probably around 8M tokens. Assuming a single fable agent that one shots the new source code at 30 tok/s, that's 74 hours. Of course it needs wayyy more tokens because it wouldn't one shot it, plus the reasoning tokens. Generation speed would be faster because you'd have many simultaneous agents though.

Bun rewrite took 6 days of coding and was a similar number of LoC, so I think a couple of weeks is definitely reasonable, although you probably need more than 5 Claude subs.