I've seen videos from Afghanistan showing US troops finding AKs buried that date from the Soviet invasion in the late 1970s. They were covered in rust and looked terrible - but were 100% operational even in that condition. Run a rod through the barrel to make sure it's clear, insert a magazine, and it still runs.

For what it's worth, the "AR family" of rifles (AR-15, M-16, M-4, etc.) actually surpass AKs in terms of field reliability and use in hostile conditions. They're built to tighter tolerances, but with the dust cover closed there isn't really any way for sand/mud/dirt to get into the action, so they continue to work.

The AK takes the opposite approach - looser tolerances and plenty of room in the action to allow foreign debris to stay out of the way and let it continue to function. You can take the dust cover off an AK, turn it upside down, and smack it a few times to knock all the junk out of the action.

AKs tend to work better with no/minimal maintenance, and are much easier to field strip and restore to operable condition. ARs require more maintenance but are easier to make (and keep) accurate, and require a bit more in terms of training and tooling to maintain under use.

I've always found it interesting that AKs are relatively easy to manufacture in rough conditions, but that ARs are easier to manufacture in the US. I can build a working AR lower receiver in the US with tools I have laying around my home (drill press, rotary tool, etc). I can't do the same for an AK because I don't have a spot welder to attach the rails. The fact that what qualifies as "easy to make" is so different depending on the environment.