Ask them. I must say, I think signing up for an ARM whether it be 3/1 5/1 7/1 10/1, you name it, is not a good idea. I know the initial lower rate is attractive, I get it. However, you need to think about the future. WHAT IF you aren't able to get a new home in 7-10 years? WHAT IF you are laid off? WHAT IF you suffer a major injury and your credit is ruined from hospital bills? Throughout the last decade, many people didn't think about these things and look what has happened now.
I would seriously consider going fixed. I used to be a mortgage broker during the hay day of the housing boom. I always recommended fixed rates. Thats just my opinion.