I have defeated all medium AIs at AI-8 (80 systems, 1 player, a variety of starting ships)
I have "semi-defeated" medium AI-9 (80-systems, 1 player, Raider), but raiders have since been nerfed
I have "semi-defeated" (Cloakmaster, Special Forces Commander) AI-10 (80 systems, 1 player, Parasite), but both Parasites and EtherJets have since been nerfed.
Semi-defeated means that I judged the game to be won, but it was simply too much work to actually play it out.