"A special, plus a new series of three episodes - it's a record-breaking run!! Of course, it's far too early to say what's coming, but we're reasonably confident that the very next thing to happen to Sherlock and John, is the very last thing you'd expect...," co-creator, writer and executive producer Steven Moffatt told PBS.
Moffatt's collaborator Mark Gatiss added, "Series Four! At last ! It's always special to return to Sherlock but this time it's even more special as we're doing...a Special! Not only THAT, we'll then be shooting three more episodes which will take Sherlock and John Watson into deeper and darker water than ever before... The whole Sherlock team are terrifically excited to return for four new adventures. The Game is on - again!"
BBC also tweeted news of the special today:
— Sherlock - #221back (@BBCOne) July 2, 2014
Cumberbatch and Martin Freeman co-star in the series inspired by the works of Sir Arthur Conan Doyle.
Cumberbatch has starred in After the Dance, Hedda Gabler and Love's Labour's Lost. He was awarded the Olivier Award, Evening Standard Award and Critics' Circle Theatre Award for his performance in Frankenstein.
Cumberbatch's film credits include "Star Trek Into Darkness" and "The Hobbit: The Desolation of Smaug" as well as "The Fifth Estate." The Golden Globe nominee also stars in "August: Osage County," the film adaptation of the Tony Award-winning play by Tracy Letts.