RE;
Fantasy.
Off season;
Occasionally there is 1 / are 2 SB Cabanas @ 120 days.
All the Family Beach Cabanas are gone before 120 days.
Good availability prior to 125 days, if you know how to ask.
Peak season;
All SB and FB Cabanas gone before 120 days.
Less availability in the summer, "prior to 125 days", even if you know how to ask.

May depend on cabin level.

Word is getting out how to book at 125 days apparently.
Shoreside is letting everyone know the rules at the same time now.
Shoreside is even educating the newbie how to book their wishes, unlike prior.
Learn the rules.
Expect more price increases. IMO
All info related to Fantasy as implied.
Of course as others have mentioned anyone can cancel, so keep an eye out.
Especially 7 - 3 days out.
I second the PP about booking CL if you want a Cabana, especially on the FB. And definitely if on the Fantasy.
I also second the PP about booking Magic Class to increase your chance for a unit.
Especially if you want a FB unit.
And fwiw to all the readers, if you haven't been to
Castaway Cay before, you don't need a Cabana.
In fact, unfortunately, even if you have a Cabana, there is a 7 - 10% chance you won't even be able to dock at CC to enjoy said Cabana, so ..... keep that in mind fwiw.
Just thought I would remind everyone again. The ship often can't dock regardless of clear skies.
Have fun,
regardless of whether you ascertained an over priced temporary shelter.
Good Luck and smooth seas to all.
Bear