Spoilers are precisely defined here. Rules vary by the story's medium. Info from television stories can't be added here until after the top or bottom of the hour, British time, closest to the end credits roll on BBC One. Therefore, fans in the Americas who are sensitive to spoilers should avoid Tardis on Sundays until they've seen the episode.
This special was not technically shown under the Doctor Who Confidential banner, though it has been generally considered an episode of the series due to the presence of Confidential's production team and its closing with the Confidential logo.