The Architect of Aeons — John C. Wright

The epic and mind-blowing finale to this visionary space opera series surpasses all expectation: Menelaus Montrose, having forged an uneasy alliance with his immortal adversary, Ximen del Azarchel, maps a future on a scale beyond anything previously imagined. No longer concerned with the course of history across mere millennia, Montrose and del Azarchel have become the architects of aeons, bringing forth minds the size of planets as they steer the bizarre intellectual descendants of an extinct humanity.

Ever driving their labors and their enmity is the hope of reunion with their shared lost love, the posthuman Rania, whose eventual return is by no means assured, but who may unravel everything these eternal rivals have sought to achieve.