I don't want to appear stupid but the latest official firmware for the AC-3200 is 3.0.0.4.378.9459, and this is the latest beta as far as I can tell or am i missing something? Wait a second, has this thread title just been amended from 9.0.0.4.378_9460 because I am getting lost.
The filename will tell the actual story. This is a beta build (version number begins with 9.0.0.4), and it's developed in parallel of the release branch, so you can't really compare version numbers between beta and release branches.