Cross Data Center travel has been something teased by the Final Fantasy XIV developers for at least 18 months. Square Enix suggested that the functionality would be included in the latest expansion for Final Fantasy XIV, Endwalker, but ultimately no solid date had been given. That is until the recent March 3 Live Letter that uses an official patch number for it's release.
Cross Data Center travel will be enabled from patch 6.18, a sub-patch of the massive 6.1 update. This will allow players to visit Worlds within different Logical Data Center, but still not beyond their Physical Data Center.
What this means is that if you are in the European Physical Data Center, you will be able to visit any world in the Chaos or Light Logical Data Center. Similarly if you’re in NA, you’ll be able to visit any world on Aether, Crystal, or Primal, and in Japan, Elemental, Gaia and Mana.
Currently there will be no travel between regions, so NA players won’t be able to visit their European friends just yet. The 6.1 patch is scheduled for release in April, with the 6.18 releasing sometime after.
For more Final Fantasy XIV guides and info, check out What are Adventure Plates? New Final Fantasy XIV 6.1 Calling Cards on Pro Game Guides.