Talk:Excalibur/Umbra/@comment-2001:8003:8663:6C00:DCE:44F2:33B6:3676-20180712071356/@comment-36003737-20180712075338

"At the end of the quest, players will receive Excalibur Umbra at rank-30 with a free, pre-installed Orokin Reactor, and Warframe slot." - Second Paragraph in Acquisition section.

You do not need an empty Warframe slot for Umbra. It comes with its own slot.