An eagle-eyed modder who goes by Chr0m3 x MoDz over at Se7enSins has discovered that in the recent 1.12 update for Grand Theft Auto V, source code has been added which allude to the existence of a jetpack.

Check out the full source code below. We've contacted Rockstar for comment and will update with anything we receive.

Since GTA V was released, one of its greatest secrets has been the Mystery of Mt. Chiliad. There are a multitude of different symbols and pictures of UFO's littered all over the game's map, but nobody has been able to fully solve the riddle. Many players believe that unlocking the mountain's secrets will reward the player with a jetpack. It now looks like one may be coming in future DLC.

http://www.ign.com/articles/2014/04/23/gta-5-source-code-alludes-to-jetpack

Code is in the link