I had my seat swapped this morning by a gate agent at ORD, and I didn't even have a chance to say no. I first noticed the change when I opened the pass on my app when boarding began and saw that my seat had changed from 4B to 1A. I asked the gate agent why, and she told me a family had asked to sit together. When I told her I chose the seat I did because I prefer not to be on the bulkhead, the response was, "Sorry, that's all we have left." Apparently I was not the only one with a surprise last minute seat change. I heard another couple asking the flight attendants during boarding why their seats had been changed.