In preparation for the launch of Pokemon Sun and Moon, the Pokemon Global Link service will come down temporarily.
The Pokemon Global Link, a feature in Pokemon X, Y, Alpha Ruby and Omega Sapphire, will go offline in late October according to the official website. The service will be updated to work with the upcoming Pokemon Sun and Moon, and when it comes back you will not be able to connect with any older games. This means the 6th generation Pokemon games will loose access to some online features permanently.
It's worth noting that two most "useful" features of the PGL - the Global Trade System and Wonder Trade - will still work. The official site has a checklist of what features will be cut, including Game Sync. This feature allows players to share medals and photos online, as well as collect items purchased with Poke Miles, an in-game currency.
To compensate, Nintendo are having a massive sale on Poke Miles. Rare Candy, Heart Scales and other items are 50 percent off from July 26 until the Global Link's discontinuation in October. Online minigames are also half off during this period.
Pokemon Sun and Moon launch November 18 on Nintendo 3DS.