"Ancient Engines" by Michael Swanwick
https://clarkesworldmagazine.com/swanwick_04_17_reprint/
A group of people at a bar in the near future discuss what traits a posthuman would require to genuinely be immortal,
“Planning to live forever, Tiktok?”
The words cut through the bar’s chatter and gab and silenced them. The
silence reached out to touch infinity and then, “I believe you’re
talking to me?” a mech said.
The drunk laughed. “Ain’t nobody else here sticking needles in his
face, is there?”
The old man saw it all. He lightly touched the hand of the young woman
sitting with him and said, “Watch.”
their hypothetical posthuman would need to be able to manufacture all its own components using only equipment built into its own body, since if it was to live forever, a statistical unlikelihood like the collapse of technological civilization would, like any non-zero statistic multiplied by infinity, be inevitable
“Apology accepted. Let’s get back to task, shall we? Our hypothetical
immortal would be a lot like flesh women, in many ways.
Self-regenerating. Able to grow her own replacement parts. She could
take in pretty much anything as fuel. A little carbon, a little water
. . . ”
“Alcohol would be an excellent fuel,” his granddaughter said.
“She’d have the ability to mimic the superficial effects of aging,”
the mech said. “Also, biological life evolves incrementally across
generations. I’d want her to be able to evolve across upgrades.”
“Fair enough. Only I’d do away with upgrades entirely, and give her
total conscious control over her body. So she could change and evolve
at will. She’ll need that ability, if she’s going to survive the
collapse of civilization.”
it would need to be able to modify itself to pass for a default human or whatever default humans evolved into to avoid being killed by any particularly xenophobic culture of default humans or evolved default human descendants.
“Also, biological life evolves incrementally across generations. I’d
want her to be able to evolve across upgrades.”
“Fair enough. Only I’d do away with upgrades entirely, and give her
total conscious control over her body. So she could change and evolve
at will. She’ll need that ability, if she’s going to survive the
collapse of civilization.”
“The year one million. Humanity evolves beyond anything we can
currently imagine. How does she respond?”
“She mimics their evolution. No—she’s been shaping their evolution.
She wants a risk-free method of going to the stars, so she’s been
encouraging a type of being that would strongly desire such a thing.
She isn’t among the first to use it, though. She waits a few hundred
generations for it to prove itself.”
The ending implies the person who brought the topic up in the first place was already such a posthuman created by a precursor civilization, gauging whether they could come out of hiding.
For a long moment the old man was silent. Then, “Thank you,” he said.
“I valued our conversation.” The interest went out of his eyes and he
looked away.
Uncertainly Jack looked at the granddaughter, who smiled and shrugged.
“He’s like that,” she said apologetically. “He’s old. His enthusiasms
wax and wane with his chemical balances. I hope you don’t mind.”
“I see.” The young man stood. Hesitantly, he made his way to the door.
At the door, he glanced back and saw the granddaughter tearing her
linen napkin into little bits and eating the shreds, delicately
washing them down with little sips of wine.
The story was written in English and collected in an anthology of short scifi stories.
"Ancient Engines" was published in a variety of places (https://www.isfdb.org/cgi-bin/title.cgi?83420) including "The Best SF 5"
