reply to Guspaz
My guess? Scale. Massive scale. For transit, they seem to have their own global internal network to run stuff through (200 gigabit between Europe and NA) with tons of transit coming out all over the place, so they can route traffic internally close to the destination and dump it into the net where it's cheapest.
For physical stuff, they didn't really do much to renovate the aluminum foundry they're in. From the pictures/videos they've released, they've built multi-storey buildings inside the existing buildings, and they seem to be using extremely high density custom form factors in custom racks (the whole racks and tower buildings are all custom purpose). Kind of like blade servers but with the entire rack being the blade chassis, except custom sized racks too. So there's just a massive economy of scale going on.
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