https://www.overclock3d.net/news/input_devices/usb-if_sheds_light_on_intel_s_thunderbolt_4_standard_-_it_s_not_a_big_leap_over_thunderbolt_3/1
 
Thunderbolt 4 was one of Intel's surprise reveals of CES 2020, but according to the hardware gurus over at the USB Implementors Forums (USB-IF), Thunderbolt 4 won't offer generational leap that users have come to expect. 

At Heise.de, USB-IF representatives have reportedly discussed Intel's Thunderbolt standard in detail at CES 2020, confirming that Thunderbolt 4 is intel's brand name for a fully-featured USB4 implementation.  Given USB4's use of Intel's Thunderbolt 3 specification, it is easy to see why Intel didn't reveal the data rates offered by the standard, aside from cryptic "4x the throughput of USB 3" comment. 

With this information, we can now reveal Thunderbolt 4 as a mere reworking of Thunderbolt 3, offering the same maximum data rates of 40Gbps. Intel's Tiger Lake series processors will release with support for Thunderbolt 4, making Intel the first company to release fully-featured USB4 products. This was always expected, given Intel's creation of Thunderbolt 3, the standard which acts as USB4's technological base. 

Thunderbolt 4 does not offer a generational performance leap over Thunderbolt 3, making the standard disappointing for those who wanted Intel to push its Thunderbolt standard further. Thunderbolt 4 is a sidestep, rather than a step forward. 

Even so, Thunderbolt 4 promises full USB4 support, which is a meaningful distinction given USB4's optional functions. With USB4, half-speed 20Gbps links are available, and PCIe tunnelling is an optional feature. Thunderbolt 4 promises that all of USB4's optional features are active, which is something that not all USB4 devices will offer. Some USB4 ports/devices will provide a maximum of 20Gbps speeds, whereas Thunderbolt 4 ports/devices are guaranteed to deliver full-fat 40Gbps link speeds. 
 
So it looks like Thunderbolt 4 isn't going to be a great leap in my opinion but rather a small step.