- Fan Nickname: The game is sometimes called "Thi4f" (Pronounced "Thi-fourth"), after the original logo when the game was still named "Thief 4".
- What Could Have Been: Many changes and additions were proposed (and scrapped) over the course of the game's five-year development cycle:
- It seems that Stephen Russell was originally intended to voice Garrett again at one point in development, as he recorded new dialogue for an unreleased trailer, but was replaced by Romano Orzari for the final game.
- A soundtrack by ex-audio director Paul Weir was completed but left unused. Judging by the track names of the songs featured within, it speaks to a very different plot for the game (including the suggestion that Erin was originally named "Ariel", and had her own theme music to boot).
- According to developer interviews, there were plans to feature a third-person perspective through the entire game, as well as environmental climbing similar to the Assassin's Creed series. The short climbing sections where Garrett is seen from a third-person perspective appear to be the only remnant of this.
- There were plans to make an experience system that could be used to level up Garrett's abilities, but this was removed and seemingly replaced with Focus Points, which upgrade various aspects of his power while using it.
- The game files make reference to two types of arrows (Phosphorus and Hammerhead) that didn't appear in the final game, as well as a set of collectibles called "Baron Statues".
- One of the tutorial help files has icons indicating that Fast Travel was planned, but never implemented.
- An unused localization folder in the game files titled "QuestJobGiverQueen" suggests that the Queen of Beggars was originally intended to be a questgiver, just like Basso, Ector and Vittori.
- There was intended to be an additional conversation during the Ector sidequest chain (likely at the conclusion of the final quest) where he would complain about the Metal Man disappearing and being locked up by the City Watch. It's still present in the game files, but is inaccessible in-game.
Trivia / Thief (2014)