The Unending Coil of Bahamut (Ultimate) was added in patch 4.11 of the Stormblood expansion.
The Unending Coil of Bahamut (Ultimate) becomes available at level 70 as part of the “Sing Me Another Song” quest, which is given by Wandering Minstrel – Kugane (X:11 Y:12).
The raid has a minimum ilevel of 0 to enter and rewards you with:
Allagan Tomestone of Poetics: 100