No assumptions, I read my contract with the mortgage co.
On the ARM--worst case scenario--I have to keep it. Given that the ARM had a low initial rate my principal has been reduced more than it would have under a conventional loan.
So each year I run interest rate risk, after the initial lock. As I did not stretch to buy the house, this is not a huge worry.
Realistic scenario--I move or refi within 5 years.
You HOPE.