Moments ago on Reddit, a user by the name of throwaway_twintania posted an image showing that their Free Company on the Moogle world had successfully completed Turn Five of The Binding Coil of Bahamut which is currently the hardest content in Final Fantasy XIV.
However, there is something else to note in this post- they were able to win due to a bug that caused the turn’s boss, Twintania to simply stand there at around 80% health allowing for an easy kill.
The OP stresses that they have already submitted a GM ticket to report the incident and due to the nature of the fight they are not claiming this to be the world first win for The Binding Coil of Bahamut.
Square Enix has previously stated that if there are issues with a monster becoming immobilized that the party should exit the battlefield and re-attempt the fight. In this case, the group in question proceeded to defeat the monster and thus complete the Binding Coil. The group has asked that they receive rollbacks as the win was unfair. Whether or not Square Enix will do that as opposed to a ban remains to be seen.