MathJax v2.0 has been officially released this morning, and is available on the CDN and for download from GitHub and www.mathjax.org. You can see the message at
https://groups.google.com/forum/#!topic/mathjax-users/naBIA_rsBdU
for more information about the release.
For the past eight months, we’ve been busy putting together version 2.0 of MathJax, which includes a number of important new features, enhancements, and bug fixes. The most significant of these are described below. Today we are releasing a public beta version of MathJax v2.0, available at
http://cdn.mathjax.org/mathjax/2.0-beta/MathJax.js
which you can load in place of the current version of MathJax that you are using.