What the Number Four Actually Guarantees

Thunderbolt 4 kept the 40Gbps link of the version before it and spent its effort on floors rather than ceilings. Where the previous standard let manufacturers ship half-speed implementations and treat several abilities as optional, version 4 made them compulsory: at least 32Gbps of PCIe throughput, two 4K displays at 60Hz or one at 8K, host charging on at least one port, and DMA protection switched on.

Those minimums are why a laptop and a dock from unrelated manufacturers tend to work together on the first attempt. The specification removed most of the room for interpretation, and with it the failure modes that dogged the earlier generation, chiefly half-bandwidth sockets and docks that could only ever drive one screen.