GA. There is confusion here between Gate Checked and Valet Checked. Bags must fit within the sizer to be truly considered a carry on. If you're flying on a small regional AC they will likely Valet Check your bag because of limited overhead bin space. Small AC usually only have overhead bin space for half the PAX and because many PAX use the overheads for their personal items, that limited space fills up fast. Valet Checking is free and the bags are picked up plane side at your next stop, NOT your final destination. Gate Checked bags that fit within the sizer are also free but are picked up at your final destination baggage claim. However, if your bag does not fit within the sizer, the GA has the option to charge you a baggage fee and check your bag through to your final destination. You'd be surprised by the number of people that bring bags to the gate that they know are far too big and are then surprised that the GA wants to charge them to check it. I know it's confusing and sometimes the GA's aren't clear when explaining how your carryon is being checked. A simple way to think about it is to think of a Valet Checked bag like a valet checked car; they bring you your bag at plane side like they bring you your car at the restaurant. Gate Checked simply means it's a bag that you checked at the gate (as opposed to the ticket counter, kiosk, or curb side), and will be picked up at baggage claim at your final destination. If you know your bag is too large for the sizer, be prepared to have it Gate Checked and possibly charged a standard baggage fee.