Both of the USB-C-enabled devices Apple has support USB 3.1. However, both the 2015 and 2016 variants only have USB 3.1 Gen 1, meaning they are basically a rebranded USB 3.0, also known as SuperSpeed USB with a maximum output of 5 Gbps.
However, a report from 9to5Mac suggests Apple is preparing new Mac hardware to support USB 3.1 Gen 2, which has a maximum output of 10 Gbps, known as SuperSpeed Plus. The finding is within macOS Sierra (beta)’s current code.
This is interesting as none of Apple’s current Mac devices sport USB 3.1 Gen 2 whatsoever, suggesting that new hardware will be released soon.
In terms of code, you can find this code in OS X El Capitan:
Versus this code in macOS Sierra beta:
A new line of code is added, specifically super_speed_plus, indicating that support for 10 Gbps USB 3.1 Gen 2 is coming very soon.
While code is software, and the software can be modified before release, this is something worth getting excited about. More specifically, Thunderbolt 3 support. Not only does it support USB 3.1 Gen 2 at 10 Gbps, but it also takes advantage of the 4x faster 40 Gbps Thunderbolt connectivity and Display Port 1.2, all in a single USB-C port that will be capable of outputs of 4K and 5K resolutions.