Info: Undead & manteinance

[Amhazair]

Originally Posted by Loren

If you spend gold for it it has upkeep. If you summon it it most likely doesn't have upkeep.

Most likely being the important part of that sentence.

To expand a bit: Any unit that can be recruited with gold will cost you upkeep, even if you summon them. This includes units that can be recruited from sites (Trolls and Sea Trolls are the most stereotypical examples) as well as units such as Yomi's Dai Oni and Kailasa's Yaksha and Yakshini, which can be summoned by later versions of their nation. If I recall correctly there are also one or two summoned units that have a goldcost associated with them (and thus cost upkeep) despite not being recruitable in any way, but I can't recall wich ones.

Also many mod nations attach a goldcost to (some) summoned units as a part of balancing.

Being undead in and of itself doesn't have an effect on upkeep cost, but since most undead units are summoned in some way they'll lack an upkeep cost.