I you look at
http://www.coin-or.org/projects/Ipopt.xml
it would appear that the current stable version of Ipopt is 3.9 and the
current release is 3.9.3.
If you look at
https://projects.coin-or.org/Ipopt/browser#releases
it would appear that the current stable version if 3.11 and the current
release is 3.11.8