I am curious about getting Cantai and have Dorico Pro 5. Will DP5 work with Cantai or would I need to upgrade to Dorico 6?
My understanding is that Cantai needs a whole bunch of features under the hood that you can only find in the latest version of Dorico…
I could try it on Dorico 5 if you really want me to, but I’m fairly confident that when both the Team and Richard da Costa tell us they have been working together in order to make Cantai work (during that last phase of the Dorico 6 cycle), they are not lying!
It is geared toward v6 of Dorico, latest updates required. There were some things in Dorico, coding wise, that required some changes in order for Cantai to function at its best. So, the best answer is probably: “no it will not work with Dorico Pro 5.”
Cantai is still very much in a development state. So, you could consider upgrading to Dorico Pro 6 whenever convenient. Then you could keep track of some of the Cantai-specific posts here to determine when you want to invest in that sound library.
These three threads probably provide the best overall picture of Cantai at the given moment. If you haven’t yet read through the entirety of the threads, I recommend taking the time to at least skim through them.
Hope this is helpful! 
Per the Cantai website, the release version of Cantai requires Dorico 6.2.20 or later.