Thunderbolt 3/4 vs USB4: Cable Compatibility Explained

Quick Answer

Thunderbolt 3, Thunderbolt 4, and USB4 cables are more alike than different, but not all are created equal. For most users, a certified Thunderbolt 4 cable offers the safest compatibility, while USB4 cables can work but may lack guaranteed features.

Why Cable Certification Matters More Than You Think

Thunderbolt 3 and Thunderbolt 4 cables look identical, but their certification guarantees different minimum performance levels. Thunderbolt 4 requires 40Gbps data transfer, dual 4K display support, and at least 100W power delivery across all certified cables. Thunderbolt 3 cables, especially older ones, may only support 20Gbps or 40Gbps depending on the cable length and build.

USB4 is designed to be compatible with Thunderbolt 3 and Thunderbolt 4, but not every USB4 cable is certified for Thunderbolt. A USB4 cable that lacks Thunderbolt certification may not support eGPU connections or full 40Gbps throughput on Thunderbolt ports. Always check for the Thunderbolt logo or explicit certification.

The 80Gbps Question: Thunderbolt 5 vs USB4

Thunderbolt 5 pushes speeds to 80Gbps, doubling Thunderbolt 4's 40Gbps. USB4, as of 2026, tops out at 40Gbps in most consumer devices, though USB4 Version 2.0 supports up to 80Gbps. If you're buying a cable for future-proofing, a Thunderbolt 5 cable is the only one that guarantees 80Gbps, but it's backward compatible with Thunderbolt 3, Thunderbolt 4, and USB4 ports.

For most current workflows, 40Gbps is still plenty for external SSDs, docks, and even 8K video. The 80Gbps jump matters mainly for high-end eGPU users and professionals working with massive files. Don't overpay for 80Gbps if your devices top out at 40Gbps.

eGPU Compatibility: A Common Source of Confusion

Many people assume any USB-C cable can connect an eGPU, but that's false. eGPUs require Thunderbolt 3 or Thunderbolt 4 ports and cables with full 40Gbps bandwidth. A USB4 cable without Thunderbolt certification may not work with an eGPU, even if the port supports it.

The safest bet for eGPU use is a certified Thunderbolt 4 cable, which guarantees the necessary bandwidth and feature support. If you're using a Thunderbolt 3 eGPU enclosure, a Thunderbolt 3 cable that supports 40Gbps will work, but verify the cable's spec before buying.

Myth-Busting Verdicts

• Myth: All Thunderbolt 3 cables support 40Gbps: False. Only Thunderbolt 3 cables certified for 40Gbps (often labeled as such) deliver full speed. Older or shorter cables may only support 20Gbps. Check the cable's spec before relying on it for high-bandwidth tasks. Look for '40Gbps' on the cable or its packaging.
• Myth: USB4 cables are always Thunderbolt-compatible: False. USB4 cables may work with Thunderbolt ports, but only those with Thunderbolt certification guarantee full feature support. For eGPU or dual 4K displays, choose a certified Thunderbolt cable. When in doubt, buy a Thunderbolt 4 cable.
• Myth: Thunderbolt 5 cables are overkill: Partly true. For current devices, 40Gbps is sufficient. But if you plan to upgrade to Thunderbolt 5 devices or need 80Gbps for high-end eGPUs, a Thunderbolt 5 cable is future-proof and backward compatible. Invest in a Thunderbolt 5 cable only if you have or plan to buy 80Gbps devices.

Product Spotlight

• Thunderbolt™ 3 / 4 and USB4 Easy Transfer Cable: The Plugable TBT-TRAN is a specialized Windows PC-to-PC transfer cable designed for direct file migration between two compatible computers with Thunderbolt or USB4 ports. It bundles Bravura Easy Computer Sync software and transfers data at up to 10Gbps. If you're migrating from an old PC to a new one, this cable avoids the need for an external hard drive and works with both Thunderbolt and USB4 ports, simplifying the process.