Depends on the airport... I tried to carry a poster tube onto an AA flight ironically a 1960 Mc’Knight Kauffer AA poster that I was having restored in LA, that I didn’t want in the hold and they weren’t having it in the cabin or taking liability for it in the hold. Paid F tickets don’t seem to carry any sway or consideration on AA these days. It’s not like they’re short of room in a F cabin with only one other seat sold, assuming they even sold it and it wasn’t an upgrade/redemption.

Tried the same thing with a TWA and a BOAC poster in Club Europe at Heathrow and they were fine. They even did a hand inspection so it didn’t need to go through the security scanner and put it in the closet. BA comes out on top, in this regard. They have always been very considerate.