Technical reference
USB4 rates, tunnels, and confidence boundaries.
Use these figures to form requirements, not to claim undisclosed product behavior or application throughput.
Public link classes
| Class | Public planning meaning | Do not infer |
|---|
| USB4 20 Gbps | USB4-class link with a 20 Gbps headline rate. | Exact optional features, display count, or application speed. |
| USB4 / Thunderbolt 40 Gbps | 40 Gbps class when mutually supported. Thunderbolt 4 certification adds documented minimum requirements. | That every generic USB4 accessory meets Thunderbolt minimums. |
| USB 80 Gbps / Thunderbolt 5 | Higher bidirectional class when host, cable, and device all support it. | Compatibility through a 40 Gbps segment. |
| Thunderbolt 5 Bandwidth Boost | Up to 120 Gbps transmit with 40 Gbps receive for display-heavy conditions. | 120 Gbps symmetric data or universal activation. |
Feature evidence
| Requirement | Evidence to collect |
|---|
| Display | Host display output/tunnel support, GPU display count, device outputs, mode payload, cable, and OS policy. |
| PCIe accessory | Explicit PCIe tunneling/enclosure support at host and device, security authorization, driver, and cable. |
| USB data | Mutual link rate plus exact downstream port rate and device interface; the fabric may carry other traffic at the same time. |
| Mixed dock | Every required feature above plus a transparent workload budget and exact dock topology. |
Windows bandwidth planning
Microsoft’s USB4 design guidance documents explicit allocation behavior, including a maximum reservation of 90% of the link in its connection-manager planning model (for example 18 Gbps on a 20 Gbps link and 36 Gbps on 40 Gbps). DisplayPort bandwidth can be adjusted dynamically, and USB plus PCIe use a shared pool. Cable Check Lab exposes the planning percentage so it is never mistaken for a universal throughput constant.
Primary sources
Use Feature Path Checker · Use Tunnel Budget Planner