I just won a defender game with 252 wave lanes. Without doing anything, just watching.
Turns out the AI is not fast enough to kill 118 systems in 15 minutes, even with more than a million ships to use.
Unfortunately I cannot tell the exact number of AI ships at the end since the galaxy statictics don't seem to show ships in carriers or barracks.
The game was diff 7/7, one neinzul, one assassin, realistic hubs 120 planet map, 118 selected, low caps, normal speed.
waves:
160k ships @ ~3min
360k ships @ ~6min
490k ships @ ~9min
750k ships @ ~12min
930k ships @ 14:50
990k ships still incoming
At the last wave the game hung for like 2 minutes on my Q6600 / 4GB RAM and afterward twice for some seconds before returning to running like a charm at 50ms performance profile. The earlier waves hung for a shorter time.
I also got some free achievements like for collecting much knowledge.
Found a bug there: if you have more than 100k available knowledge, the last digit isn't shown.
Another one: according to the statistics, I had -2000 surviving ships at the end.
During all that time, Ai Wars never needed more than 1.5 GB.