Vault is an ability granted by the Icarus Armor and possessed by some enemies (MECs; Leap for Chryssalid, Faceless).
Vault allows a soldier to move to any elevated surface within movement range without the need to use a ladder or other climbing utility. Vault is a passive ability that does not require activation and has no cooldown. It triggers automatically and does not break concealment, provided the soldier does not traverse an observed tile.