Which cable is designed specifically for 40GBASE-T?

The cable designed specifically for 40GBASE-T is Cat 8 cable. Cat 8, which is the latest standard in twisted pair cabling, supports Ethernet speeds of up to 25 Gbps and 40 Gbps over a distance of up to 30 meters. It is intended for data centers where high-speed communication is critical and is compatible with network switches and other equipment designed for such high speeds.

The other options, while capable of supporting high-speed networking, do not have the specifications or performance characteristics required for 40GBASE-T. Cat 6 and Cat 6a cables are generally used for 10GBASE-T applications, with Cat 6a being able to support 10 Gbps over longer distances than Cat 6. Cat 7, although also rated for high speeds, is not officially recognized as a standard for Ethernet in the same way that Cat 8 is. Thus, for applications demanding the performance associated with 40GBASE-T, Cat 8 is the appropriate choice.