I left it up to the imagination of the reader. It could be one of our minds after an imperfect cloning, modified by someone for "efficiency." It could be super-optimizing AIs. Tens of thousands of years from now, thousands of light-years distant, who knows what it will be like?

Why cloning? Gradual replacement seems the way to go.

If you transform rather than duplicate yourself, it doesn't matter if you're still 'human'. What matters is that you're alive and conscious.

It seems the consensus in this subthread is that gradual replacement involves a potentially unsolvable philosophical problem, unlike cloning. How can you be sure you remain you during gradual replacement, and don't turn into some kind of a philosophical zombie?