There were AI before Gaia...kind of? Horus is described as a "high-speed learning machine network." So maybe not a complete AI, but a precursor? Just seems crazy if Gaia is their first AI, considering how advanced and kind-of amazing she is.
I guess Horus could have been a precursor but for Gaia to be a self aware AI to know what they're and to be able be it's own person in a way... That's incredible how much they got right on their first try!