I can’t find this mentioned anywhere (or whether it’s 32-bit).
For anyone who has it installed, you can check by going to Applications → Utilities → Activity Monitor. Right-click (command-click) on the column headers and make sure that “Kind” is checked. Under the kind column, in the avast row(s), it will either say “Intel” (meaning 32-bit), or “Intel (64-bit)”. If they all say “Intel (64-bit)”, then it’s 64-bit. If any just say “Intel”, then it’s not a fully 64-bit app.
The fact that it is 32b is a GOOD thing, it uses LESS memory by just not being 64b, I can’t see any of 64b benefits making a positive difference on avast!, for instance, the ability to use more than 4 GB memory for its process, why would avast need to use 4 GB of memory?
Well, there are more components that are 32bit only at the moment - setup, submitter and diff (but they can be quite easily made universal 32/64-bit).
There could be few advantages of having native 64bit engine, large file mapping and faster scanning routine, for example - but yes, 64-bit hype is a bit overrated phenomenon, I agree :).