Eigen 3.3.1 has been released today, on December 06, 2016.
This is a maintenance release with few bug fixes and performance regressions since the first release of the 3.3 series. This release also includes better cmake support (imported targets, relocatable package). For more details, look at the changelog: http://eigen.tuxfamily.org/index.php?title=ChangeLog#Eigen_3.3.1 .