The Clarett interfaces use Thunderbolt 1. Thunderbolt 1 has a bandwidth of 10 Gbps which is more than enough bandwidth for audio recording and other applications. For example, 64 channels of audio recorded at 192 kHz would amount to roughly 280 Mbps, not even scratching the surface of the 10Gbps bandwidth of Thunderbolt 1.
Thunderbolt 2 has two 10 Gbps bi-directional channels and combines them into a single 20 Gbps bi-directional channel. The amount of information that can travel through the Thunderbolt connection has not increased rather the throughput of a single channel has doubles. This is helpful when dealing with massive amounts of data such as 4K video.
Clarett interfaces can be connected to either Thunderbolt 1 or Thunderbolt 2 ports.