What's the difference?

Strictly speaking we should be comparing Thunderbolt 3 with USB 3.2. Many people use the term USB C to describe both the function of the interface and the connector. However USB C actually only describes the connector style (properly called the USB Type-C connector) whereas USB 3.2 defines the functionality. A USB C connector is small and can be plugged in regardless or orientation.

Thunderbolt 3 also uses the USB Type C connector with functionally that is a superset of USB 3.2. Thunderbolt 3 does everything USB 3.2 does and more. Thunderbolt 3 has a maximum transfer rate of up to 40Gbps whereas USB 3.2 has a maximum transfer rate of 20Gbps. Both can power devices like laptops and displays at up to 100W (20V/5A) with USB Power Delivery technology. 

What do I have, USB C or Thunderbolt 3?

Because both technologies utilise the same physical connector and port markings can be inconsistent, it can be hard to tell. The latest Apple devices (2017/2018 onwards) utilise ThunderBolt 3 and many Windows laptop manufacturers also now support it, albeit not on all models. Chromebooks are less likely to utilise Thunderbolt 3 technology.

We strongly recommend you check the specification of your computer to determine which standard it supports. 

How about compatibility?

Simply put, if your computer (host device) supports ThunderBolt 3 then it is also by definition compatible with USB 3.2 peripherals. However the reverse is not necessarily true.

Depending upon the specification, a host device supporting USB 3.2 with DP1.4 Alt Mode or DP 1.2 Alt Mode can support some Thunderbolt 3 peripherals but with reduced specifications..

What's next?

ThunderBolt 4 and USB 4.

USB 4 will require the use of the USB Type-C connector and support data transfer rates up to 40Gbps. In turn Thunderbolt 4 will again be a superset of USB 4 and a Thunderbolt 4 host will be compatible with USB 4 peripherals.