In preparation for Pokémon Sun and Moon, the Pokémon Global Link will be discontinued for the Generation 6 Pokémon games (X, Y, Omega Ruby, and Alpha Sapphire) this October. After the closure, features such as Game Sync, the PokéMileage Club, and Rating Battles will no longer function. As a farewell gift, starting Tuesday, July 26, 2016, and running until ceasing of operations, the following perks will be enacted: all attractions will be half price, several useful items will be going on sale, and the Ability Capsule will be available to purchase for 5,000 Miles.
The Global Trade Station (GTS), Wonder Trade, and Free Battles will be unaffected by the discontinuation.
The Global Link for Pokémon Sun and Moon is due for launch on November 18, 2016.
UPDATE: the Global Link will be closed at midnight on November 1, 2016.
Source:
Pokémon GL Official Site