I'm looking for a short story I've found as a PDF on the Internet once, but I can't remember the name anymore and therefore can't find the story:
It mostly follows a (bodily) young women, who turns out to be an old woman whose body has been optimized by a self-learning, basically all-controlling AI whose aim is to follow the wishes of and protect humankind.
In this story, the AI gains more and more knowledge (e.g. medical know-how to optimize the human body) and learns first to control all kind of machinery (e.g. solar cells to power everything), and then to change/control everything at an atomic level.
Humans basically can't/won't be allowed to die, but there is this 1-on-1-battle-game, where you order the AI not to interfere for 12 or 24 hours, which this woman is good at and plays a lot.
Humans can live out most of their wishes, since the AI tries to accommodate them. And it protects/helps them by e.g. "folding away" (on an atomic level) and "storing" alien civilisations.
The story also roughly follows the question of "when is a human not human anymore" - people whose only "activity" is to have their pleasure center stimulated are first seen by the AI as humans, but not anymore at the end of the story.