RAW and RAI were addressed in the other answers, no, it does not make an AoO for using its reach.
It only makes sense when the creature is so massive that its appendages can be considered individually for an attack.
I once created/used a monster that had extensible tentacles. It was a Gargantuan creature, but its bulky, amorphous body (I think it was some sort of mutant deepspawn) sat in the back of the 150' square room. It had 100' reach with those tentacles and could make 8 attacks each round with them with unlimited AoO (still only once per target) in a round, but tentacles needed to move into the space of the target in order to attack / grapple /
do hentai stuff.
So a character in the path of a tentacle could try and cut a tentacle using her own AoO. If the tentacle HP dropped to zero, it would be cut and the attack wasted. It would allow for tanks/DPS to protect the support characters. You could attack the tentacle coming for you if you triggered an AoO too.
I can't get the statistics right now, but the tentacles were very squishy (low AC for its parent's CR and also about 12 HP each), could regrow in 2 rounds.
It made for a very interesting boss battle, and an epic tactical scenario, with the melee combatants deliberately provoking AoO in order to slice tentacles, and the paladin strategically positioning himself in order to protect the spellcasters' movement path.