USB Interface History

The major USB speed improvements are shown on the below timeline.

Fully backwards compatible

Each successive generation is fully backwards compatible with previous versions. Older devices always work in newer sockets and newer devices always work in older sockets, albeit at the slower speed.

Current and proposed speed increases

Currently USB 3.1 Gen 2 devices can reach speeds of up to 1,250 MBps. USB 3.1 was finalized in 2014, when maximum transfer speeds doubled  from 625 MBps to 1,250 (matching Thunderbolt). Maximum power output also increased from 10 to 100 watts and a new reversible C type plug was introduced. These upgrades to the specification were entitled USB 3.1 Gen 2 rather than USB 4.0.