Two laptops sit on the same purchase order. Both list USB-C ports. Both come with a dock that claims USB4. The cheaper one cannot drive the two monitors the dock was bought for, and nothing on either datasheet explains why.
This is not a hardware fault. It is a specification that allows a very wide range of products to use the same name, sitting next to a certification programme that does not.
Who Owns What
The relationship is easy to state and hard to remember.
USB4 is a specification managed by the USB Implementers Forum. It was built on the Thunderbolt protocol specification contributed by Intel, and it complements the existing USB 3.2 and 2.0 architectures. It uses the USB Type-C connector, runs two lanes, supports up to 80 Gbps operation over 80 Gbps certified cables, and stays backward compatible with USB 3.2, USB 2.0 and Thunderbolt 3 hosts and devices.
Thunderbolt is an Intel trademark and an Intel-managed verification programme. USB4 is a USB-IF trademark. Two different organisations, two different logos, and — this is the part that matters on a purchase order — two very different promises.
One more detail worth keeping straight: Thunderbolt 3 predates USB4 and is not a USB4 product, even though USB4 hosts are backward compatible with Thunderbolt 3 devices. If a supplier describes a Thunderbolt 3 accessory as "USB4", they have the generations tangled.
Where the Minimums Diverge
Here is the comparison that ends most arguments. These are Intel’s own published minimum requirements.
Capability | USB4 | Thunderbolt 4 | Thunderbolt 5 |
|---|
Minimum data bandwidth | 20 Gbps | 40 Gbps bidirectional | 80 Gbps bidirectional |
|---|
Bandwidth Boost (asymmetric) | Optional | Not applicable | 120 Gbps, dynamically allocated |
|---|
Display output requirement | One display, no minimum bandwidth | Dual 4K displays | Dual 6K displays |
|---|
PCIe data tunnelling | Optional, with no performance requirement when implemented | 32 Gbps required | 64 Gbps required |
|---|
PC charging | Not required | Supported, for PCs up to 140W | Supported, for PCs up to 240W |
|---|
Wake from sleep | Not required | Required and tested | Required and tested |
|---|
DMA security protection | Not required | Required | Required |
|---|
Independent certification | Optional — self-declared compliance | Required for all products | Required for all products |
|---|
Cable quality audits | Not required | Required | Required |
|---|
Read the USB4 column again, because it is the one people skip.
A product can carry a USB4 logo with as little as 20 Gbps of data bandwidth, no guaranteed display support, no PCIe performance requirement, no charging requirement, and no wake-from-sleep testing. Intel’s own framing is blunt about the gap: USB4 defines what a product *can* support, while Thunderbolt certification validates what a product *has been proven* to deliver.
That is the whole trade. USB4 gives manufacturers room to build cheap, legitimate, genuinely USB4 products. Thunderbolt closes that room by making the best features mandatory and independently verified.
For a fleet buyer, this produces a specific and useful difference. Every Thunderbolt port on a certified PC meets the same bar — there is no need to work out which port is the good one. A USB4 machine may have one full-featured port and others that are considerably less than that.
The Cable Is Where the Money Goes Missing
If you only take one thing from this article, take this: two USB-C cables can look physically identical and deliver completely different results. One carries full bandwidth. The other silently downgrades data speed, caps display resolution, or fails to deliver adequate power — and nothing on the outside tells you which you are holding.
Three things help.
Thunderbolt Certified cables carry the icon and a technology number — 3, 4 or 5 — stamped directly on the connector. That single marking tells you the cable was tested for bandwidth, signal integrity and power delivery, and that the manufacturer is subject to cable quality audits so production consistency does not stop after the first batch.
USB-IF requires labelling on all USB-C to USB-C cables. Every qualifying cable must be marked with a power capability of either 60W or 240W using the appropriate icon, and every cable except USB 2.0 must also be marked with the data rate it supports. The example USB-IF gives is a 20 Gbps cable rated 20V at 3A, carrying the combined 20Gbps/60W logo. The markings are checked before compliance testing begins, and a cable that fails is not authorised to bear the logos at all.
Length catches people out at the top end. USB4 uses the USB-C connector at up to 40 Gbps, and the recommended maximum passive USB-C cable length for it is 0.8 metres — about 2.6 feet. That figure applies to the 40 Gbps cables and to the USB4 80 Gbps specification cables as well. Active versions stretch to about three metres, which is a large improvement over 0.8 m and still nowhere near the lengths people assume.
The mechanism behind that, for anyone who wants the why: USB is duplex and waits for a response before sending the next packet. Longer cable means longer round trip and more chance of a late collision. Every increase in data rate leaves less time for that response, so newer USB generations get *shorter* maximum cable lengths, not longer. If a two-metre USB-C cable is expected to carry 40 Gbps in your design, that expectation needs revisiting.
Power: Where the Numbers Actually Change
USB-C charging numbers have moved twice, and old figures are still quoted as current.
Before the USB PD 3.1 update, USB Power Delivery was limited to 100W, using 20V over cables rated at 5A. The 3.1 revision, announced in 2021, raised the ceiling to 240W over a full-featured USB Type-C cable and connector, adding fixed voltages of 28V, 36V and 48V to deliver 140W, 180W and 240W respectively. The USB Type-C specification was updated to Release 2.1 to define the 240W cable requirements.
Against those ceilings, the Thunderbolt requirements sit like this: Thunderbolt 4 requires charging support for PCs up to 140W; Thunderbolt 5 raises that to 240W. USB4 requires no charging capability at all.
So if a project depends on one cable powering a workstation over the same link that carries display and data, the specification you actually need is the certification, not the connector. And the cable must carry the right number printed on it — a 240W requirement cannot be met by a cable marked 60W, however well it is made.
Three Things Buyers Get Wrong
The connector shape tells you nothing about capability. USB-C is a physical standard. USB4 and Thunderbolt are capability tiers that happen to use it. A portfolio of matching USB-C ports can contain ports with dramatically different ceilings.
"Compatible" is not "certified." Intel states plainly that Thunderbolt certification is not a self-declared marketing claim and not a paid licence fee — it is third-party testing of complete system behaviour, including sleep, wake and reconnect, across multiple brands and generations. A product described as "Thunderbolt compatible" has told you nothing verifiable. Look for the logo, and check the product against the certified products database.
One USB4 port does not mean all of them. Since minimums are optional, a machine can legitimately carry the logo and still have ports that will not do what your dock needs.
Our own USB4 cables and USB 3.1 Type-C cables are built to stated performance, not to a shape, and test and inspection covers how we verify them before shipment. If the project includes docking, the USB hubs and docking stations page sets out what we build, and the certifications we hold lists what we can evidence.
What to Put on the Purchase Order
Specification failures are usually procurement failures. Eight line items cover most of them.
- The required bandwidth in one direction, written as a number. "USB4" is not a number. "40 Gbps bidirectional" is.
- The number of displays, with resolution and refresh rate for each. Display support is optional under USB4 and mandatory under Thunderbolt 4 and 5, so this is the line item that decides which logo the project actually needs.
- The PCIe bandwidth the application depends on. Where storage speed matters, 32 Gbps on Thunderbolt 4 or 64 Gbps on Thunderbolt 5 is the floor to compare against. USB4 carries no performance requirement even when PCIe tunnelling is implemented.
- The charging wattage, stated at the device. Say so explicitly if it is above 100W, because that is where the USB PD 3.1 revision and the 240W cable requirements begin to apply.
- The certification you will accept as evidence, and which database you will check it in. Self-declared compliance is a defensible answer for some projects and unacceptable for others — but it should be a decision rather than an accident.
- The cable marking, required in writing. Power marking and data-rate marking on every USB-C to USB-C cable, plus the Thunderbolt icon and technology number wherever Thunderbolt certification is required.
- The cable length you actually need, against the passive limit. 0.8 metres passively at 40 Gbps, around three metres with an active cable. Beyond that it is an extender question, not a cable question.
- What has to happen at sleep and wake. If the dock must recover without someone unplugging it, that behaviour is required and tested under Thunderbolt and not required under USB4.
Frequently Asked Questions
Is Thunderbolt 4 faster than USB4?
Not necessarily in peak terms — both can reach 40 Gbps. The difference is the floor. Thunderbolt 4 guarantees 40 Gbps bidirectional; USB4 permits as little as 20 Gbps.
Can I use a regular USB-C cable for USB4 or Thunderbolt?
For low-speed work, sometimes. For 40 Gbps or 80 Gbps operation over any real distance, the cable has to be built and certified for it. USB4’s own documentation refers to 80 Gbps operation over 80 Gbps certified cables.
Does a Thunderbolt 3 device work on a USB4 host?
Backward compatibility with Thunderbolt 3 hosts and devices is supported on USB4. What you get is the best mutual capability of the two devices, which may be well below either one’s maximum.
How do I check whether a specific product is really certified?
Two public checks: read the marking on the physical product — Thunderbolt cables carry the icon and a technology number on the connector, and USB-C to USB-C cables must carry a power marking and, above USB 2.0, a data-rate marking — then look the product up in the relevant certified products database before the order is placed.
The Short Version
USB4 is the specification; Thunderbolt is the certification built on top of it. USB4 defines what a product may support and permits a low floor. Thunderbolt makes the strongest features mandatory and has them independently tested.
If a project depends on display count, PCIe storage speed, wake-from-sleep reliability or high-wattage charging, buy the certification rather than the connector. And read the cable marking before you buy the cable, because that is where an otherwise correct specification quietly collapses.
The two laptops from the opening are not a hardware mystery. One was specified against a logo, the other against a set of numbers. Only the second one works.
If you are specifying a USB4 or Thunderbolt programme and want to confirm what we can build, mark and certify for it, send us the details — bandwidth, power and the certification the project requires — and we will tell you what fits. For custom connector configurations, see our Type-C conversion cables.
Sources
- USB-IF — USB4, including the relationship to the Thunderbolt protocol specification contributed by Intel, two-lane operation and 80 Gbps certified cables — https://www.usb.org/usb4
- USB-IF — USB Charger (USB Power Delivery), including the PD 3.1 update to 240W, the prior 100W limit, the 28V/36V/48V fixed voltages and the Release 2.1 cable requirements — https://www.usb.org/usb-charger-pd
- USB-IF — Cables and Connectors, including the mandatory USB-C to USB-C power and data-rate labelling requirements and the compliance-testing sequence — https://www.usb.org/cable_connector
- Intel — Thunderbolt Certified: Why It Matters for Reliability & Performance, including the minimum capability table for USB4, Thunderbolt 4 and Thunderbolt 5, the connector marking and cable quality audits — https://community.intel.com/t5/Blogs/Products-and-Solutions/Connectivity/Thunderbolt-Certified-Why-It-Matters-for-Reliability-Performance/post/1750714
- Thunderbolt — Certified Products Database — https://www.thunderbolttechnology.net/products
- Cable Matters — USB Cable Max Length, including the 0.8 m recommended passive limit for USB4 USB-C cables, the three-metre active limit, and the late-collision mechanism — https://www.cablematters.com/Blog/USB-C/usb-cable-max-length
- USB-IF — USB4 Specification v2.0 — https://www.usb.org/document-library/usb4r-specification-v20
