The writer-producer said Sherlock Holmes will be seen in a new light in the special segment, reported Entertainment Weekly.
"Sherlock is a little more polished. He operates like a Victorian gentleman instead of a posh, rude man. He's a lot less brattish," he said.
Moffat also revealed that Martin Freeman's character, Dr Watson, will be "more uptight".
The special episode of "Sherlock" will see stars Cumberbatch and Freeman travelling to the Victorian England.
The time travelling, however, will not be explained in the episode.
The episode, whose release date is yet to be announced, is independent from the show's highly anticipated fourth season, which will likely appear in 2016.
