The USB Promoter group announced the specifications for USB4 in March 2019, but now the USB Implementors Forum has published the finalised version which means device manufacturers can start producing USB 4 peripherals and other gadgets.

When is USB 4 coming out?

Developers and manufacturers can now download the published specifications, but it will be at least another year before we start seeing USB4 appear in consumer products, so it will be late 2020 or early 2021 before you’ll have to worry about it.

USB4, which has no space in its official name, will bring a range of improvements to USB 3.2. USB4 is based on Thunderbolt architecture which doubles the bandwidth of the current USB technology so it can run at 40Gbps and can handle multiple data and display protocols at the same time. 

This is the latest reversible USB. There aren't as many accessories as you'll find with USB-A, but an extra Type C port can be used for data and, if labelled as such, for pass-through power delivery from a USB-C wall charger.  Make sure you check the USB speed rating when choosing your hub, as they range from 480Mbps to 40Gbps.

Fortunately, nothing will change physically, so while the underlying tech will be different, USB4 cables and ports will look exactly the same as existing USB-C. But of course, it will boast data transfer speeds equivalent to Intel's Thunderbolt 3 version of USB-C.

Given that USB-C still feels relatively new, yet another version of USB arriving sounds a little daunting. But it's good news overall.

How is USB 4 different to USB 3.2 and USB 2?

  • Up to 40Gbps data transfer speed using two-lane cables, matching the speed of Thunderbolt 3
  • Better video performance thanks to the technology intelligently allocating resources based upon transfer demand
  • Thunderbolt 3 compatible depending on how the USB 4 technology is implemented
  • Will use Type-C ports
  • Backwards compatible with USB 3.2, USB 2 and Thunderbolt 3

What are the different versions of USB-C?

The USB standard is a bit of a mess at the moment. You've got different types of physical port, and even if you look only at USB-C ports, there are different standards which use them, such as USB 3, 3.1 and 3.2. The USB-IF has said that it won't do this for USB4, and that if it ever goes faster, it will be called USB5.

Here's an explanation of each USB standard.

  • SuperSpeed USB aka USB 3.1 Gen 1 aka USB 3.2 1: 5Gbps
  • SuperSpeed USB 10Gbps aka USB 3.1 Gen 2 aka USB 3.2 2: 10Gbps
  • SuperSpeed USB 20Gbps aka USB 3.2 2x2: 20Gbps
  • Thunderbolt 3: 40Gbps
  • USB4 (coming in 2020): 40Gbps

USB-C specs

Is USB 4 compatible with Thunderbolt 3?

Intel, the developer and owner of the Thunderbolt 3 protocol, has provided it to the USB Promoter Group to allow the upcoming USB4 platform to be compatible with Thunderbolt 3 devices. While this is great news for consumers generally, manufacturers will not be obliged to implement Thunderbolt 3 functionality into their USB 4 specs, so you could well end up with a USB4-enabled device that won’t be compatible with Thunderbolt 3. As ever, it’s important to check the exact specification of the device you’re purchasing before you put down your hard-earned money.

While the promise of 40Gbps transfer speeds looks great on paper, not every USB device will be able to meet that speed, so USB4 devices might have to lower their speed to accommodate the hardware they're connected to. There will be three speeds available to USB 4 (10Gbps 20Gbps and 40Gbps) and you can usually expect the smaller and less expensive devices to be capped at the lower transfer speeds.

Intelligent bandwidth sharing

USB-C introduced a feature called “alternative mode” which allows input from DisplayPort and HDMI from a USB-C port, but the current technology doesn’t allow for an efficient way of splitting resources if you’re also transferring both data and video at the same - it will divide the bandwidth between the two streams of information granting 50% bandwidth to each.

USB 4 will intelligently allocate resources to video and data streams based on demand, so if you’re streaming 4k video and transferring files at the same time, the technology will do its best to balance these needs out to keep both data streams running smoothly.

USB4 Power Delivery

Only certain USB-C ports support USB Power Delivery (USB-PD), which is a requirement for charging some devices including laptops. Every USB4 device and port will support USB-PD as standard with the ability to support up to 100 Watts, although no charging device will provide anything close to that amount of power just yet.

USB4 will also be backwards compatible with USB 3 and 2 devices, although you will be limited to the speed of the older versions if they do interact. A USB4 external drive will not gain USB4 speeds if it is connected to a device via a USB 2 or 3 port.


If you're still struggling with the switch from USB-A to USB-C then getting an adapter will make your life much easier.