The other option is to take one more year of arbitration then if he continues like extend him the QO and maybe get another year or draft pick
This would be my preference over a 3-4 year extension right now. I believe in his game and the changes he's made. It looks sustainable through his early 30's just like Charlie Morton.
The Twins have the luxury of one more arbitration year with him. He's at $4.5 million now, and with the wins and losses not going his way, he'll be pretty cheap again for 2019. Probably in the $8-9 million range?
There's nothing wrong with taking this one year at a time and seeing what happens. If he's still awesome all the way through 2019, the Twins have a great problem to deal with.