Yes. 'Harry Potter and the Cursed Child' is considered canon by J. K. Rowling, and it was marketed when published and premiered as the eighth Harry Potter story. While many Harry Potter fans do not consider 'Harry Potter and the Cursed Child' as canon because of how different and underdeveloped it is in comparison to its prequels, it still remains an important addition to the canon of Harry Potter stories told because of how closely related it is to the characters and events of all the previous books.