They mention in the article that GDDR5 is embedded "on chip", which presumably means on package.
>AMD has updated its press release to state that it is the GDDR5 controller that is on the chip, and not the 8 GB of GDDR5. The memory is installed on the board elsewhere, as with a normal GPU for example.
Also they now have a newer article with photos: https://www.anandtech.com/show/13163/more-details-about-the-...