USB4
A USB standard (2019) built on Intel's donated Thunderbolt 3 protocol. Uses only the USB-C connector, up to 40 Gbps (USB4 v2: 80 Gbps, 2022). Can tunnel DisplayPort and PCIe. Notorious for confusing optional feature labeling.
The confusion: almost everything in USB4 is optional — a "USB4" port can be 20 or 40 Gbps, may support PCIe tunneling, may not. Thunderbolt 4 is essentially USB4 with a strict mandatory feature floor (40 Gbps, PCIe, dual 4K). USB4 v2 (80 Gbps) is the basis for Thunderbolt 5. Distinct from USB 3.2 (an older naming mess, no tunneling). The industry is heavily criticized for the labeling chaos (USB-IF even retroactively renamed old standards). Advice: look for concrete numbers (Gbps, W) and logos, not just "USB4". Backward compatible via USB-C with older USB + DisplayPort alt-mode.