Take a peek at the table of contents of Journeys Through the Radiant Citadel (as shared by BoLS). The book contains the 13 adventures we already know of, a chapter introducing the citadel itself, and a chapter of stat blocks. The hardcover comes out next week, after some production delays.
WotC has shared the credits page of the Journeys Through the Radiant Citadel. The book was written by a team of people of colour. In their press release WotC said that "Journeys through the Radiant Citadel is a collaboration between the D&D team and a talented collection of artists...