Class Relics, also called Subclass Artifacts, were items which used to unlock character subclasses. They were removed from the game.
Each character class used to have two Class Relics, with the first available at level 8+ and the second available at level 15+.
Once obtained, a Class Relic was placed into a spot the subclass it unlocked would be accessed from. Hovering over it would reveal a progress bar that could be filled by defeating enemies and participating in Public Events.
After the player charged a Relic, they could access a special Shard of the Traveler mission in the EDZ. During this activity, the player would learn more about the subclass they are about to unlock and fight off enemies. The subclass would be properly unlocked after completing the mission, and it used to have all grenades, movement, class abilities and the Super available from the beginning, while subclass trees had to be unlocked with Upgrade Points.
As of New Light, the Class Relics are no longer available and every subclass is unlocked from the start of the game.