According to The Radio Times, the Sherlock Holiday Special will air on January 1st, 2016. The news comes from the mouths of show architects Steven Moffat and Mark Gatiss during their appearance at MCM London. Producer Sue Vertue added, "it will go out in America on the same day."
The special episode, which sees Benedict Cumberbatch and Martin Freeman playing Holmes and Watson in the characters' original Victorian setting, will be called "The Abominable Bride." Gatiss explained the title comes from Watson's reference to "Ricoletti of the club foot and his abominable wife," a case Holmes and Watson undertook, but author Sir Arthur Conan Doyle never wrote about.
In the states, PBS has released a new trailer for the special: