https://www.nationstates.net/nation=mechanica_rationalis
3 billion, which I've just brought back after like 4 months of inactivity and no nation growth. Social utopia with universal free healthcare, exceedingly powerful information tech sector, and bristling defensive abilities. Mechanica Rationalis is the most technologically advanced nation in the Democratic Council of Hollow World, and has, on top of the 3 billion human population, a thriving number of fully sapient machines which live and work alongside humans. Recent advancements in nanotech have resulted in a cultural revolution, with the old guard preferring to keep using their macroscopic synthetic implants and the younger generation investing in and using nanite enhancement to become true post-humans.
Humans are split into several different social classes in Mechanica Rationalis based not on income (since there's a 90% income tax) but on the level of investment into integration with the synthetic population which is far larger than the human side. People regularly swap their biological parts for mechanical alternatives, or supplement their bodies with new and powerful tech. There is no need for humans to work at all as machines can supply everything they need, and so the level of investment into posthumanism determines a person's social class.
Mechanica Rationalis first started off as a machine only nation with a single citizen, Mechanica itself, a refugee from a far-future alternate Altera where Grief was eventually destroyed by Hawklight tech. Mechanica was the sole surviving AI of an escape attempt from a doomed world forgotten by gods and kings (the Tekkit server way into the future) and faced vastly diminished operational capacity upon arriving in NationStates!Earth. Only recently has tech begun to approach the old levels, and the economic boom and constant technological expansion led to humans emigrating from their homelands to live in Mechanica Rationalis.
In recent times, Mechanica has started an initiative to plumb the depths of the planet while working on several orbital and deep space projects. The current capital city from which Mechanica rules is the Orion Complex, a manufacturing facility several miles underground and the largest of its kind, pumping out thousands of synthetics every day. In orbit, the capital/colony ship of MRCS Forward Unto The Light is under construction. Upon completion, Mechanica will divide its consciousness and send this backup of itself into interstellar space along with a full complement of the most advanced synthetics and the cream of the crop of the humans and post-humans.
Mechanica itself is not located in any single place but exists instead through borrowing the processing power of every synthetic and post-human inside the borders of its nation as well as using miles and miles of constantly improving processor banks.
Now step aside and let the adults talk.