After carefully reading the description of Ioun Stones, I am left wondering if they are suppose to be considered attended objects or not. This is of course for the free floating version, not ones that have been inserted into a wayfinder which would clearly be attended.
Reasons for why they could be considered unattended objects
- Item description does not directly mention they are attended
An ioun stone must be able to orbit freely around a creature’s head for its power to be active
- They have their own AC which I cant think of another attended object which has its own AC
Reasons for why they could be considered attended objects
- No listed saving throws for the purposes of AoE's which suggests they are suppose to use their owners
Overall there isnt any strong evidence in either category by my thoughts. Personally I would side with them being attended objects since that's how I have always treated them, and it was only recently that I considered otherwise.