With the Battle for Azeroth expansion for World of Warcraft on the horizon, Blizzard is beginning to slowly phase out some Legion-specific features starting with artifact weapons. Don't worry, you can still use them for now, but a blog post details that Magni Bronzebeard is summoning players to Silithus where they'll use the power of their artifact weapons to "draw out the darkness from Sargeras’ sword and help stabilize Azeroth’s grievous wounds."
If you're not up to speed on Warcraft's story, when players defeat Sargeras in the latest raid, he plunges a continent-sized sword into the planet, which makes for a pretty awesome cutscene. This sword is becoming a central part of the prologue story leading up to Battle for Azeroth.
Players who venture to Silithus will "destabilize" their artifact weapons, granting them a temporary boost in power but also setting the stage for them to be retired when the Battle for Azeroth pre-expansion patch launches. Once that happens, you'll still have your artifact weapon, but the powerful traits that actually make it worth using will be deactivated. This is, of course, a big change but one that Blizzard made players aware of many months ago.
Artifact weapons aren't the only things slowly being phased out in preparation for the new expansion. As the blog post describes, The Mage's Tower on the Broken Shore will now be active 24/7 so players can beat its trial and unlock that oh-so-cool unique artifact weapon skin.
Likewise, a bunch of achievements are being turned into Feats of Strength once the pre-patch launches—Blizzard's way of effectively retiring them and their rewards. That means you only have a few weeks left to earn certain mounts that drop from the latest raid.
You can find a full list of the impending changes in this blog post. World of Warcraft: Battle for Azeroth launches on August 14, but a pre-patch will bring a lot of exciting changes before then.