@zhanghm18 The desire to build an experimental unit is almost identical between the factions, so I'm guessing it was different game-states that led to UEF building lots and Cybran not.
The choice of what experimental to build will vary though. The logic is based on unit categories, and if the desired category isn't available then the AI will switch to building a random experimental. What that means in practice is that if for example you have a mod that adds a bunch of land experimentals to the game, and M28 wants to build a land experimental, it will pick from any of the existing FAF and new modded experimentals.
If instead M28 wants to build say a novax and the mod removes novax but adds a new air experimental, then M28 will switch to building any random experimental (which will include the modded experimental as an option).
In terms of the unit cap M28 should already adapt to getting near the unit cap, e.g. it should ctrl-K T1-T2 units, not build more T1-T2 units (with a couple of rare exceptions), and stop building a particular type of unit that it has lots of (regardless of tech level). If it is actually hitting the 1k unit cap consistently I'd need a replay to assess, as adding logic to not build any T3 units at a certain point could have significant drawbacks - for example, if it stopped building asfs it could quickly lose air control and then it wouldn't matter how many land experimentals it built if they'd just die to enemy gunships/strats.