The new legendary armor set is planned for release in the second major update following the expansion’s launch. You’ll be able to begin working toward it on August 22, though—crucial components will be available to acquire, and you’ll be able to start training your Astral Ward Masteries to unlock crafting recipes. Part of the necessary steps for completing your legendary armor will be completing the Astral Ward and Rift Hunter’s armor collections.

This is from the blog post on the gw2 website.

You can actually see most of the requirements through achievements and new crafting recipes, look through new SOTO collections