From Halopedia, the Halo wiki
Halo: Outcasts is an upcoming print novel by Troy Denning, set to be released on May 30th, 2023. The novel was originally set to release on October 18, 2022, but was ultimately delayed due to Denning's own personal health complications.
The novel follows Thel 'Vadam and Olympia Vale's efforts to recover a rumored artifact on Netherop that could stop Cortana, unaware that they're being manipulated by someone else. The novel's focus on Netherop follows on from the planet's establishment and heavy feature in previous Denning novels Silent Storm and Oblivion.