The Heart of Thorns series does not have a new book coming out soon. The latest book, Soul of Cinder (Book 3), was published in January 2021.
The first book in the Heart of Thorns series, Heart of Thorns, was published in September 2018.
The Heart of Thorns series primarily falls into the Fantasy genre. This young adult series was written for ages 12-17, but can be enjoyed by adults too.