If you did a 6-year contract, do you have to spend the whole 6 years at your 1st duty station?

No, you only have to do 3 years at a duty station. As you get closer to that mark, you can call your branch manager and ask to move. If you're willing to go airborne, it's even sooner.

It also depends on the type of unit you’re assigned too. Depending upon if the unit is a rotational unit, you can be “fenced in”, meaning you would have to get approval from the Brigade CSM and/or the BN CDR. I personally know a quite a bit of SM who have been at the duty assignment 5yrs plus due to being fenced in.

it happened to me. I spent 5+ years on Ft. Bliss. I eventually came down on orders to Korea though. But I was the only soldier of my mos in a unique unit.