If I exercised ISO's in 2005 at a price of $8 with a FMV of $23, paid AMT and sold the stock in 2018 for $50, am entitled to an AMT credit?

[TomYoung]

Well, you could be, yes, though it's not "automatic" in the sense that "I paid AMT when I exercised but I'll get it all back when I sell."  It's a little more complicated then that.   Use the ISO "Guide me step by step" process to report your sale.  That will put the correct "reversing" entry on Form 6251.

Tom Young