Eigen 3.3-alpha1 has been released today, September 4, 2015.
The source archive is at:
This alpha version introduces a novel evaluation mechanism of expressions, as well as numerous exciting features such as fast divide and conquer SVD [1], support for AVX and VSX vector instructions, more OpenMP parallelism [2], a LS-CG solver [3], and more. Check the page dedicated on the 3.3 release [4] for a comprehensive review of the novelties and improvements.
As for any alpha and beta release, everybody is invited to test this release on their own basecode and report any compilation issues or performance regressions on the bugtracker [5].