New Machine (All Tomorrows)

The New Machines were a robotic posthuman species that was created from the Gravital by the Asteromorphs.

When the Asteromorphs won the war against the Gravital and repopulated the milky way with Subjects and Terrestrials, they didn't completely destroy the Gravital. They planned it at first, but saw that their abilities were to valuable because they were able to live in the most inhospitable conditions.

So the Asteromorphs remade the Gravital into the New Machines by removing their ability of gravital manipulation, giving them shorter lifespans and slightly numbing their imagination to prevent another uprising like that of the Gravital. But they also gave them nanotechnological bodies that were able to constantly remake themselves as they wished or needed for their jobs.

Even though they were widespread in the new empire, the machines were always rare and treated as second class citizens by the biological citizens, because history gave them a deep distrust regarding their mechanical relatives.

By the time of All Tomorrows afterword, all of humanity has disappeared for unknown reasons, maybe it got extinct through a war or the empire slowly fell apart, leaving single colonies to face their own fates each. Maybe, it was a mass migration to another plane of existence. The fictional, nonhuman Author of the book doesn't know.