I did not really understand the apparent massive gains -- even the example about controlling concurrency in terms of chapter count seemed weird because the Java example passed info about chapter purpose; the Python one was just `write_single_chapter()` and seemed to have no context.

To be honest, I also really dislike the idea of using AIs to write books. It seems absolutely emblematic of the AIs replacing creativity, authors and artists side of AI -- antisocial tech, tech as anti-all-that-is-good-in-humans -- whereas AIs can be of great benefit when used to augment positively. IMO it says a lot when someone chooses that sort of example.

Isn't this just some loops and joining with some changes in prompts?

Can't you write this in a for loop calling the open AI API directly?