Hacker News Reader

4GB of 1600MHz LPDDR3 memory

Configurable to 8GB or 16GB, only at the Apple Online Store.

That means that you can't go to a physical Apple Store and buy one with more than 4GB of RAM, not that you can't personally install more RAM.

Seems that new generation of apple's hardware comes with RAM welded, being un-upgradable after "bought".