New beta build! https://wiki.arcengames.com/index.php?title=AI_War_2:Multiplayer_Alpha_And_Beta#Beta_2.766_Huge_Multiplayer_Speed_Boost
You need to use the current_beta branch on Steam or GOG to play this one. If you have trouble with it, there is a most_recent_stable_beta, now, too.
This one introduces a new mod that lets you basically just have nothing but frigates, and it includes some more buffs to frigates in general.
After that, there's a really huge speed boost to multiplayer networking, most notably if you are on Steam (but also present on GOG and elsewhere). The Steam networking was actually the most used, but also the most laggy, so now it has caught up to the others and they have all leapt forward.
The short explanation is that there are many ways to interact with Steam's networking (four main ones), and the primary one that I chose turned out to be suboptimal for our particular use case. One of the nice things about running a beta. I switched from their "connection oriented" multiplayer model to their entirely-separate peer-to-peer model, and the results are staggeringly better. I am temporarily leaving the connection oriented steam multiplayer in as an option, but I'll probably comment out its xml entry if everyone is having good success on P2P.
The second part of the explanation is that -- partly now due to this shift -- we are able to run with multiple parallel data channels, rather than having a single lane for all data. If you imagine this like a highway, this shifts from being two lanes to being eight lanes -- with literal fast lanes that are all that is needed to keep the game moving. The slower traffic can take its time and it doesn't hurt anything.
If this solves the bulk of the lag that people are seeing -- and it should -- then this may mean that multiplayer is very very close to being full production ready. I'll wait until May to call that final, and fix bugs that pop up in the meantime. But it's feeling SO smooth. Enjoy!