I have version 16 Apprentice, I really like Houdini and am thinking about purchasing the Indie version. If I buy it now I get 16.5, when it come around is the upgrade to 17 Indie free?

Best to ask support just to make sure, but yes I'm pretty sure it's based on time ( yearly subscription ).

I was on 15.5 when I upgraded to Indie.

16 came out before my 1 year was up and I didn't have to dish out extra to use 16

Indie is an annual subscription. So if H17 comes out within a year of H16.5 then you will get the upgrade license as part of your subscription.

Thank you Robert.