Why this answer matters
A USB-C connector alone does not prove 40-Gb/s operation. Slow docks, cables and USB-only devices can make a Thunderbolt 4 port appear slower while the Mac is functioning normally.
2 requirements3 verification steps1 primary source
Requirements
What has to be true
- Thunderbolt 4/USB4-capable device and cable for a 40-Gb/s class link.
- No lower-speed hub or adapter inserted in the path.
Verify it yourself
Use this test sequence
Change one variable at a time so you know which requirement made the difference.
- 1
Check the peripheral's actual interface class.
- 2
Test directly with a certified high-speed cable.
- 3
Separate display, charging and storage complaints because they negotiate independently.
Limits
What this answer does not prove
- 40 Gb/s is interface bandwidth, not guaranteed file-copy throughput.
- Some devices use fewer PCIe/USB lanes or slower internal media.
Relevant DeviceOK checks
Test the part you can observe
Data Transfer Time CalculatorEstimate ideal transfer time from data size and an entered link rate.
→USB-C Display Path Readiness CheckCheck four documented prerequisites for sending video through USB-C, Thunderbolt, a dock, cable or adapter to a display.
→USB-C Cable Power Rating CheckCompare an entered cable wattage rating with the power you want to carry, while keeping protocol/e-marker limits explicit.
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