OAK 4, a major upgrade to the product, was released on 8 April 2009.
The latest version of OAK, version 4.20.022, released on 26 June 2012, is a minor update to OAK 4.20.009.
If updating OAK is costly for you, e.g. due to lengthy corporate approval processes, you are recommended to wait for OAK 4.3, which is still in testing.
Users of prior versions of OAK 4 will be automatically offered the chance to install the new version by OAK’s automatic updating feature.
There is a detailed version history of OAK in the online documentation.