Read the official Contao announcements.
Contao 3.3.RC2 is available
by Leo Feyer – Announcements
Contao version 3.3.RC1 is available. Please do not use beta versions for productional websites! Download the release to check whether your website or custom extension needs adaptation.
We had to remove the "index a page via Ajax" feature due to an unforeseen error and replace it with a different implementation. However, since fixing the bug required to adjust a very central part of the system, namely the template system, we have decided to publish another release candidate for testing purposes.