It wouldn’t be a true celebration if we didn’t show some love to the community that’s supported us all these years. When you log in on August 23, you’ll find a new series of achievements waiting for you that will take you on a journey to experience the best of Guild Wars 2: world bosses, Guild Wars 2: Heart of Thorns, Guild Wars 2: Path of Fire, Guild Wars 2: End of Dragons, Living World, World vs. World, Player vs. Player, and more. As you complete these tasks, you’ll earn Proofs of Legend, which can be traded in for the new Decade armor set. These achievements are permanent additions to the game. As is traditional, we’ll also have a wide range of Gem Store sales to celebrate the anniversary, and maybe even a few freebies to collect (spoiler: mount skin).
https://www.guildwars2.com/en/news/studio-update-guild-wars-2-tenth-anniversary-and-steam-launch-on-august-23/