Explainer
USB4 vs Thunderbolt 4 vs Thunderbolt 5, explained
· Cablyst
Four standards, one connector. USB4, Thunderbolt 3, Thunderbolt 4, and Thunderbolt 5 all use USB-C, all overlap, and all get printed on packaging with cheerful imprecision. Here's what each actually guarantees — and why the only number that matters is the one that's active on your port right now.
The short version
- USB4 is the base standard. It allows 20 Gbps or 40 Gbps, and makes several features (like PCIe tunneling) optional. "USB4" alone doesn't promise the top tier.
- Thunderbolt 4 is a strict superset of USB4: it requires 40 Gbps, PCIe tunneling, and dual-4K (or single-8K) display support. If it says Thunderbolt 4 and it's genuine, those guarantees hold.
- Thunderbolt 5 raises the ceiling to 80 Gbps symmetric, and up to 120 Gbps in the asymmetric "Bandwidth Boost" mode for displays, plus higher power.
- Thunderbolt 3 is the older 40 Gbps generation, still everywhere in docks and cables.
Why the label lies (a little)
The negotiated link depends on the weakest of three things: the host port, the cable, and the device. A Thunderbolt 5 Mac with a Thunderbolt 3 cable negotiates a Thunderbolt 3 link. A "USB4" cable might only run 20 Gbps. The packaging describes a best case; the port describes reality.
The standard on the box is a ceiling. The active link is the truth.
See what's actually active
Cablyst reads the negotiated link straight from macOS and names it — Thunderbolt 3/4/5, USB4, or plain USB — along with the lane configuration and the cable's e-marker tier. Its Negotiation Diagnostics show what the port, cable, and device each support versus what was agreed, with the weak link flagged. That's how you find out the $20 cable is quietly capping your $4,000 setup at 20 Gbps.
Want the real, hardware-level answer for your own cable? Install Cablyst or get Pro ($9.99 lifetime).