16 GB is its maximum RAM capacity, currently. The chipset in that MBP can probably take 32 GB RAM, but as no 16 GB SO-DIMM modules exist yet, you are limited to 8 GB
204-pin DDR3 SO-DIMM RAM modules.
As for Apple stating only 8 GB as its maximum, that is Apple's MO for a lot of Macs, not stating the correct RAM maximum.
EveryMac and MacTracker can tell you the real RAM maximum for every past and current model, if you are interested in more proof.
PS: If you decide to upgrade RAM from the base model, look at Newegg for RAM modules, as that is often cheaper. 16 GB can be had for less than 100 USD nowadays.