Arround 2010, there were some rumors that Avast was working in porting its antivirus to Win64 plattform. Unfortunately this is not the case even with 2016 beta.
A feature that is available since years ago in other vendors such as Bitdefender, and others using its engine like Comodo.
To me it is a pitty, since according to my tests, there is a slight about 10% performance improvement with x64 as comparison to x86.
I certainly can’t recall this ever being in the forums - the reverse in fact - the avast installation process detects if you have a 64bit OS then any required 64bit functions, low level drivers will be used.
As I recall, it has been mentioned in numerous topic (by avast staff) that a completely 64bit program wouldn’t bring significant performance improvements.
Since avast doesn’t have a native 64bit OS I don’t see how you can say that there is no 64bit version of avast to test.