It is also not a simple replacement for the old system, but instead a complete revamp, including an all-new rewards list.
The Infinity Chest is located at the Soul Room (accessed with the ::soulroom command).
When you open the chest, it will visually scroll through all the rewards. Once it stops, you must manually pick up your reward (as if it were on the floor), and then start again.
The Infinity Chest in action.