I don't think they are "officially" supported... still. That being said, we have done several stacked via boards without issue. No clearance/connectivity errors but when you gen the NC Drill it throws a warning and changes the smaller holes in the stack to be the same as the largest in the stack... if I remember correctly.
You can do a simple board with the structures you need, and run that through your process to see if the results are acceptable.
Thanks Chuck. So, you don't need to play the "offset the vias" game?
No we stack them at the same X, Y.
There is a quick and easy way about it and very simple.
For stacked micro vias (L1-L2, L2-L3), define it as L!-L3 and fab shops
will drill it L2-L3 and L1-L2..
Hope this works for you.