USB4 vs Thunderbolt 4: Same Cable, Different Guarantees
USB4 was built on Thunderbolt 3. Intel contributed the protocol to USB-IF, so the two share a physical layer and a 40 Gbps ceiling. The difference is not speed. It is which features are required rather than optional.
What is mandatory in each
| Feature | USB4 | Thunderbolt 4 |
|---|---|---|
| Max data rate | 20 or 40 Gbps (either is compliant) | 40 Gbps required |
| PCIe tunneling | Optional | Required, 32 Gbps minimum |
| Display support | DisplayPort 1.4a minimum | Dual 4K or single 8K required |
| Minimum host power | 7.5 W | 15 W |
| Wake from sleep | Optional | Required |
| DMA protection | Optional | Required (VT-d) |
The line that matters for buyers: a compliant USB4 port can be 20 Gbps with no PCIe tunneling. So “USB4” on a spec sheet does not guarantee 40 Gbps or eGPU support. Thunderbolt 4 does, because Intel certifies against a fixed floor.
For cables specifically, the distinction nearly vanishes
A passive 40 Gbps USB-C cable that passes USB4 certification will carry Thunderbolt 4 traffic. The cable does not implement PCIe tunneling or DMA protection; those live in the host and device controllers. What the cable must do is hold signal integrity at 20 GHz per lane.
Practically this means:
- Passive, up to 0.8 m — standard construction, most cost effective
- Passive, 1 m — needs tighter impedance control, coaxial construction typical
- Active, above 1 m — redriver or retimer silicon in the connector head, notably more expensive
Our USB4 lines are coaxial construction, rated 40 Gbps with 100 W PD, CE FCC EMC ROHS ISO9001.
The 240 W question
USB PD 3.1 raised the ceiling to 240 W (48 V, 5 A). This is independent of the data tier: a 240 W cable can be USB 2.0 for data, and a 40 Gbps cable can be limited to 60 W.
When a buyer says “USB4 240 W” they are asking for two separate qualifications. Confirm both. Combining top-tier data with top-tier power raises cost more than either alone, because the conductor gauge that carries 5 A at 48 V works against the geometry that keeps 40 Gbps clean.
What to put in an RFQ
- Data rate: 20 or 40 Gbps, stated explicitly
- Power: 60 / 100 / 240 W, with e-marker confirmation
- Video: DisplayPort Alt Mode version and max resolution/refresh
- Length, and whether passive or active at that length
- USB-IF certification with TID
- Whether Thunderbolt logo use is required (that is an Intel certification, separate cost and process)
The last point catches people out. Putting the Thunderbolt logo on retail packaging requires Intel certification, not just USB4 compliance. If your customer needs the logo, that is a different program with its own lead time.
Choosing in practice
If the end use is a docking station, external NVMe, or a display, a certified 40 Gbps USB4 cable does the job and costs less than a Thunderbolt-branded equivalent. If the end use is an eGPU or the retail box needs the Thunderbolt logo, go Thunderbolt and budget for the certification.
