Minecraft wiki entry for Development_versions, associated text: Added the Swift Sneak enchantment.
This enchantment can be found exclusively in chests in Ancient Cities.
Cannot be obtained by fishing, enchanting, or other loot chests, similar to Soul Speed.
Has three levels.
Can only be applied on boots.
Is incompatible with Soul Speed, Frost Walker, or Depth Strider.
Allow the player to walk faster while sneaking, up to 75% of normal speed at level III.