From the website: iPerf3 is a tool for active measurements of the
maximum achievable bandwidth on IP networks. It supports tuning of
various parameters related to timing, buffers and protocols (TCP, UDP,
SCTP with IPv4 and IPv6). For each test it reports the bandwidth, loss,
and other parameters.

This is a new implementation that shares no code with the original
iPerf and also is not backwards compatible. iPerf was orginally
developed by NLANR/DAST. iPerf3 is principally developed by ESnet /
Lawrence Berkeley National Laboratory.