I just finished an LLM assisted Rust rewrite of a production project after a couple months. It's around 150k LOC, mostly Rust, excluding generated code and tests. Around 200k if I include tests. I'm also now starting to extract / refactor some of it's code into their own reusable crates, so my LOC isn't going to grow and might even shrink a bit. I can't speak to 1M LOC, but I'd imagine that takes a lot of human context to reason about too, and you probably want to break it up into manageable chunks if possible.

LLMs have been a boon. I have a lot of guardrails in place though to keep the LLMs focused and producing correct and ergonomic code. A lot of effort and review has gone into creating these guardrails (choice of language, linting, forced conventions, tests, etc.). A lot of these practices will be useful in future projects. I highly recommend this approach. Don't just copy skills or processes that others publish. Figure it out yourself so the lessons stick. Human in the loop, especially one that has learned through practice and failure, is still immensely valuable IMO. It's a fine line between getting stuff done and yakshaving over your tooling... but that's always been the case, as proven by my vim dotfiles. :)

It's worth noting that the AI industry is filled with tons of snakeoil and BS. You don't need to take someone's course in "21 steps to be productive with AI" or w/e. Just like learning a new programming language, dig right in and try to build something that scratches an itch. Pick a project you have complete autonomy over instead of that "spend all the tokens" crap managers were pushing until recently (this has corrected now right?).

Parent saying "Skill issue" though... What a jackarse.