The 4e Modron Article

Since it's significant enough for Planescape, I'll give a short summary for those who can't access subscription material off of the WotC site.

So a lot of the old background is still there, they still come from Mechanus, they still do the Great Modron March (though the schedule is described as unknown), there's still base and hierarch Modrons. The Modrons statted out are Monodrones, Duodrones, Quadrones and a generic stat block for all Hierarch Modrons, though it's probably a Decaton. The only picture in the article is of a Quadrone with a halberd standing on a ledge in Sigil.

What's changed is that Modrons are described as being like cells of Primus, and that they're made up of multiple numbers of lesser Modrons. In fact if any of those Modrons die, they tend to split up into Monodrones (which are minions). But it's different in that they're mentioned as combining into greater Modrons or separating into lesser ones as their needed. Modrons still go rogue, but it apparently requires all the Modrons that are pieces to go Rogue too, before a higher level one goes Rogue.

It also leads to Modrons apparently being against portals which cause the entropy of the multiverse and are much like the Per in guarding them, probably because of the change in 4e's alignment fluff. Here they are described as being enemies of the Slaadi, which was never outright mentioned before but only suggested from what I remember.

With Primus they never mention its death at the hands of Orcus/Tenebrous. They've said Primus' origin is "Hard to know" but suggest that it might be a Primordial that was simply mechanical. And that the cycles of the Modron March might have to do with Primus disassembling and reassembling itself.