Ironic isn't it? The most useful service and (... no seeds, no stems, no sticks))) nobody knows nothing about the way they operate. They gotta use something to generate btc wallet addresses for the registered users aren't they?
Of course they do... but it is a proprietary, closed-source system. So it isn't at all strange that no one knows what they're doing or how they're doing it outside of the coinbase development team
It's like they store everything in a system, each user is randomly assigned one or more bitcoin addresses, I don't think it's arbitrary, but it's the same way we create a new address in Electrum. I assume they own an wallet similar to Electrum, and they use it to create a series of addresses and allocate to users. The amount of money transferred to the users' addresses will be automatically transferred to another address, their source address. Just speculation
