I have got a 2017 Trek Fuel EX 5. After Christmas I may be upgrading it with a dropper seatpost.
I would like to know if it is compatible with an internally routed dropper seatpost.
You could check if you have a hole to insert the droppers cable/hose into the frame. It should either be in the seattube ( which would include some kind of cable guides on the downtube ) or somewhere around the headtube. If one of these is available you are good to go.
Apart from that I can't think of any newer frame which isn't compatible with internal dropper posts. Therfore it should fit just fine.