Thunderbolt 4 vs USB4: which 40 Gbps port should you trust for big transfers?

How they differ

A certified Thunderbolt 4 port is guaranteed to deliver 40 Gbps and 32 Gbps of PCIe tunneling, which is what an external NVMe SSD enclosure uses to reach near-native speeds. A USB4 port can do the same, but it doesn't have to - the spec lets manufacturers ship 20 Gbps USB4 ports with weaker or absent PCIe tunneling. In practice a full-featured USB4 port, like the ones on Apple Silicon Macs, matches Thunderbolt 4 and copies a terabyte at the same rate. A bare-minimum USB4 port can run at half that and the label won't warn you. The tell is the documentation, not the logo: if the port isn't explicitly listed as 40 Gbps with PCIe support, assume the floor.

Verdict

Both standards top out at 40 Gbps, so a full-featured USB4 port and a certified Thunderbolt 4 port copy 1 TB in the same ~3m 20s on a fast NVMe drive. The difference is the floor: Thunderbolt 4 mandates 40 Gbps and 32 Gbps of PCIe tunneling on every port, while USB4 permits a 20 Gbps implementation with optional PCIe. So the verdict is a tie at the top of the spec, but Thunderbolt 4 wins on predictability since the badge itself certifies the speed you actually need.