Open a laptop’s USB-C port in 2026 and you cannot tell from the connector alone whether it is a basic USB 3 port, a USB4 port, a Thunderbolt 4 port, or a Thunderbolt 5 port. They all look identical. The same cable will physically plug into all of them. The capabilities, however, can vary by an order of magnitude. A Thunderbolt 4 port supports two 4K displays plus an external GPU at PCIe gen 3 x4 speeds; a USB-C-only port from 2019 supports one 1080p display and an external SSD at 5 Gbps. This guide walks through what Thunderbolt 4 and USB4 actually are, what each is required to support, and how to read your device’s spec sheet to know what you can actually plug into it.
A short history of how we got here
The cable-and-connector confusion exists because USB-C is a connector spec, not a protocol spec. USB-C arrived in 2014, designed to carry many different protocols (USB, DisplayPort, HDMI, Thunderbolt, audio) over the same connector. The connector won universal adoption; the protocols on the connector remained a free-for-all.
Thunderbolt 3 launched in 2015 as Intel’s high-end protocol on the USB-C connector: 40 Gbps, PCIe tunneling, dual 4K display support. Thunderbolt 4 followed in 2020 with the same bandwidth but tighter requirements. USB4, announced in 2019 and shipping widely from 2021, is a follow-on standard that adopts much of Thunderbolt’s technology and runs on the same connector.
Today the four common USB-C protocol levels are:
- USB 3.2 Gen 2 (10 Gbps)
- USB 3.2 Gen 2x2 (20 Gbps, less common)
- USB4 (20 or 40 Gbps, varies by implementation)
- Thunderbolt 4 (40 Gbps mandatory, dual 4K mandatory, PCIe mandatory)
- Thunderbolt 5 (80 Gbps base, 120 Gbps burst)
What Thunderbolt 4 requires
Thunderbolt 4 is a certification, not just a spec. To label a port “Thunderbolt 4,” the device must support:
- 40 Gbps maximum bandwidth
- Two 4K displays at 60 Hz, or one 8K display
- PCIe tunneling at 32 Gbps
- USB4 compatibility (40 Gbps mode)
- DisplayPort Alt Mode 1.4
- Wake from sleep on a connected device
- Charging at up to 100W (some 240W on TB4 v2)
- 0.8 meter passive cables certified to 40 Gbps; up to 2 meters with active cables
A device that ships with the Thunderbolt 4 logo has passed Intel’s certification and is guaranteed to support all of these features.
What USB4 allows
USB4 is more flexible and consequently more confusing. The spec allows but does not require:
- 40 Gbps (some USB4 ports cap at 20 Gbps)
- PCIe tunneling (optional)
- Dual 4K display support (optional)
- 100W charging (optional, varies by device)
This means two USB4 ports on two different laptops might have substantially different capabilities. A USB4 port on a 2026 ThinkPad X1 Carbon might match Thunderbolt 4 feature-for-feature. A USB4 port on a budget Chromebook might cap at 20 Gbps with no PCIe support.
USB4 v2.0 (announced 2022, shipping 2024+) doubles maximum bandwidth to 80 Gbps, matching Thunderbolt 5. As with USB4 v1, the higher bandwidth is allowed but not required.
Reading a port’s actual capabilities
Manufacturers in 2026 are required by the USB-IF to label USB ports with their performance levels, but the labels are inconsistent and often appear only in the spec sheet rather than on the device itself.
What to look for:
- “Thunderbolt 4” with the lightning bolt logo: full TB4 capabilities guaranteed
- “USB4 40Gbps”: full 40 Gbps, but display and PCIe support uncertain
- “USB4 20Gbps”: half bandwidth
- “USB 3.2 Gen 2x2”: 20 Gbps, no PCIe, limited display options
- “USB 3.2 Gen 2”: 10 Gbps, basic data and DisplayPort Alt Mode
- “USB 3.1” or “USB 3.0”: 5 Gbps or 10 Gbps depending on era
On a Mac, all USB-C ports on M1 to M3 generation MacBook Pros are Thunderbolt 4. On M4 generation MacBook Pros (shipped late 2024+), the Pro and Max models include Thunderbolt 5.
On PCs, check the specific port. Many laptops mix one or two Thunderbolt 4 ports with one or two regular USB-C ports.
The cable problem
USB-C cables are deceptively unequal. Two cables that look identical might support:
- USB 2 only (data at 480 Mbps, charging at 60W)
- USB 3.2 Gen 1 (5 Gbps, 60W or 100W)
- USB 3.2 Gen 2 (10 Gbps, 100W)
- USB4 (20 Gbps, 100W)
- USB4 / Thunderbolt 4 (40 Gbps, 100W)
- Thunderbolt 5 (80 Gbps, 240W)
The cable that came in the box with your phone might be USB 2 only. Plug it into a Thunderbolt 4 port and your “Thunderbolt 4” connection runs at 480 Mbps.
In 2026 the USB-IF has rolled out certified labels showing speed (5G, 10G, 20G, 40G, 80G) and power (60W, 100W, 240W). Cables certified for the higher tiers tend to cost $25 to $80 for short lengths, more for active cables.
A practical rule: keep one or two Thunderbolt 4 (40 Gbps, 100W) cables in the bag and use them for everything. The slight cost premium pays back in not troubleshooting cable mismatches.
What each protocol actually enables in practice
eGPU (external GPU enclosure): Requires PCIe tunneling. Thunderbolt 3, Thunderbolt 4, or USB4 with PCIe support. A plain USB 3.2 port cannot run an eGPU.
Dual 4K monitor docking station: Thunderbolt 4 guarantees support; USB4 may or may not. Plain USB-C usually does not.
Fast external NVMe SSD (above 1,000 MB/s): Requires 20 or 40 Gbps. USB 3.2 Gen 2 caps you at 1,000 MB/s.
Single-cable laptop dock (one cable for power, video, ethernet, all USB peripherals): Thunderbolt 4 or USB4 with PD and display support.
Daisy chaining (one Thunderbolt device into another into a display): Thunderbolt 4 only. USB4 does not specify daisy chain behavior, and most USB4 docks do not support it.
What to buy in 2026
If you are buying a laptop in 2026, Thunderbolt 4 or Thunderbolt 5 ports are the safer choice. The cost premium is small (often $50 to $150 for a TB-equipped model vs the USB-C-only equivalent) and the capability gap is large.
If you are buying a desktop or motherboard, look for Thunderbolt 4 cards or motherboards with TB4 onboard, especially if you want to run pro-grade external storage or dual monitors from a single cable.
For external storage on either protocol, see our NAS storage uses guide. For the wireless side of fast networking, our Wi-Fi 7 real-world speeds article covers the radio-link equivalents.
Frequently asked questions
Are Thunderbolt 4 and USB4 the same?+
Not quite. They share the same connector (USB-C) and the same 40 Gbps maximum. Thunderbolt 4 mandates the high-end features (40 Gbps, dual 4K displays, PCIe tunneling, 32 Gbps PCIe, daisy chaining); USB4 allows them but does not require them. A USB4 port might only deliver 20 Gbps with no PCIe support and still be a valid USB4 port.
Will a Thunderbolt 4 cable work with a USB4 port?+
Yes. Thunderbolt 4 cables are backward compatible with USB4, Thunderbolt 3, and USB 3.2 ports. A Thunderbolt 4 cable plugged into a USB4 port operates at the port's capability ceiling, not the cable's. The reverse (a USB4 cable in a Thunderbolt 4 port) usually works but may not reach 40 Gbps unless the USB4 cable is certified for 40 Gbps.
Why is Thunderbolt 5 already coming out?+
Thunderbolt 5 (announced 2023, shipping in 2024+ Macs and select PCs in 2024 to 2026) doubles bandwidth to 80 Gbps and supports up to 120 Gbps in burst mode for high-resolution displays. It is the same connector but with new silicon. Thunderbolt 4 remains the mainstream tier; Thunderbolt 5 is the high-end.
Do I need Thunderbolt for an external SSD?+
Only if you want speeds above 1,000 MB/s. A USB 3.2 Gen 2 (10 Gbps) external SSD reads at about 1,000 MB/s, which is the same as the fastest internal SATA SSD. To exceed that (1,800 to 3,400 MB/s on top external NVMe enclosures), you need Thunderbolt 3, Thunderbolt 4, or USB4 at 40 Gbps.
Can I run two 4K monitors from one USB-C port?+
Thunderbolt 4 ports are required to support dual 4K at 60 Hz. USB4 ports may or may not, depending on implementation. USB-C-without-Thunderbolt-or-USB4 ports (some Chromebooks, older laptops) generally support one 4K display, not two. Check the spec sheet for 'dual display' or 'DisplayPort Alt Mode 1.4'.
Taylor Quinn
Taylor Quinn writes for The Tested Hub.