USB4

Universal Serial Bus 4 (USB4), sometimes erroneously referred to as USB 4.0, is the most recent technical specification of the USB (Universal Serial Bus) data communication standard. The USB Implementers Forum announced USB4 in 2019.

USB4 enables multiple devices to dynamically share a single high-speed data link. USB4 defines signaling rates of 20 Gbit/s, 40 Gbit/s and 80 Gbit/s. USB4 is only defined for USB-C connectors, and its Type-C specification regulates the connector, cables, and basic power delivery features across all uses of USB-C cables, enhanced with the USB Power Delivery specification.

The USB4 standard mandates "functionality backward compatibility" to USB 3.x and dedicated backward compatibility with USB 2.0. The dynamic sharing of bandwidth of a USB4 connection is achieved by encapsulating multiple virtual connections ("tunnels") of other protocols, such as USB 3.x, HDMI, DisplayPort and PCI Express.

USB4 is based on the Thunderbolt 3 protocol. However, it is different enough that backward compatibility to Thunderbolt 3 is optional for many device types.