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.
Clarett interfaces can be connected to either Thunderbolt 1 or Thunderbolt 2 ports directly, or a Thunderbolt 3 port when using an Apple Thunderbolt 3 to Thunderbolt 2 adapter.
If you wish to use a Clarett Thunderbolt interface on a Windows system then please read this article.