It's been auto renew for a while.
Sure came as a surprise to me! (Is this one of those deals where you have to tell Sony not to auto-charge every time you buy a subscription? Because that bugged the piss outta me with Microsoft.)
Pretty sure you can turn that off, or never have it on by un checking the box when you sign up.
PS+ has always been a great deal for me. Live on Xbox.... Meh. It used to be the best, then Sony joined the fight, game over.