The USB Implementers Forum has announced the publication of USB4! The specification is available to download now as part of the document library of USB.org.
USB Implementers Forum Announces the Publication of Its Thunderbolt 3-Based USB4 Standard article tells that USB 4 offers up to 40Gb/s throughput, PCI Express, and DisplayPort connectivity — plus compatibility back to USB 2.0.
USB4 is built around Intel’s Thunderbolt connectivity standard, which incorporates PCI Express and DisplayPort plus power delivery connectivity in a single cable.
USB4 is promised to be be fully backwards compatible with previous USB devices from the current top-end USB 3.2 Gen 2×2 standard down to USB 2.0 (though not now very rarely used USB 1.0). USB4 will be compatible with existing USB Type-C cables.