I just came off of an Alaskan flight. I used the Exo K2 frame which stands about 24" give or take and it WOULD NOT fit in the overhead compartment. I had to shift the pack sideways along with the other carry on's to get it to fit. I removed the belt/lid and kept it as small as I could (hunting clothes/optics only) and no one questioned it. Flight attendants did not see me shift it sideways and i closed the overhead bin when I was done as it was full. They were good about checking our carry on bags for free on my flight. Possibly be prepared for that.
You can usually check it at the gate for no fee if you want to load it up. Just make sure you have a lid/pocket to put your optics/etc in so you can carry them on.