Nothing is spawned. AI empires have corporations that try to make profit using game mechanics.
Example:
AI empire wants to build a military ship. Spawn one? No! It collects its taxes and orders a ship from the shipyard company. That is what an empire is supposed to do, collect taxes and build military ships.
The shipyard company now with money from the empire and an order starts building the ship. It now needs to get the materials so it starts buying materials until fulfilled. If it doesn't get fulfilled it will raise the prices. That's what shipyard companies are supposed to do, sell ships and buy construction materials with the money.
The freighter company sees this and will set trade routes between suppliers and the shipyard in it's optimized trade route network (one thing ai should be good at). With the new profits from these trades it will use the money to build new freighters, which is what a freighter company is supposed to do, fulfill price imbalances and buy more freighters with the profit.
The shipbuilding materials station has been sitting on a full cargo hold with no buyers until now. So they lower the prices and stop buying iron. Then they are visited by a freighter destined for the shipyard and it takes it all. Now they have a low inventory and more money. They raise the price of its output and start buying iron. If iron does not arrive, it will raise the price of iron. That's what shipbuilding material companies do, they sell shipbuilding materials and use the money to buy iron. If it has enough extra credits it will found a new station.
Since the shipbuilding materials company has increased its price for iron, freighters are now visiting miners to fulfill the price imbalance. The miner company uses the extra money to build more miners because that's what miner companies do, they sell iron and buy more miners with the money.
The universe could have the Dwarf Fortress backstory generator and each empire starts with one drone at Prime and it builds it's fleets and stations from there. When you start you can choose the age of the universe you want, from just starting to build the first spaceship and empty to developed and full.