What was the working title of Assassin's Creed during its early development?

The early working title of Assassin's Creed was Prince of Persia: Assassins.

The project began at Ubisoft Montreal as a proposed spin-off connected to the Prince of Persia series. Its concept centered on a bodyguard serving a prince, but the idea evolved into a larger game about secret orders, historical assassination, and free-roaming cities. As development continued, the project became its own franchise.

The final Assassin's Creed game retained some design influences associated with Prince of Persia, particularly fluid climbing and acrobatic movement. It also developed new systems involving social stealth, investigations, memory sequences, and the Animus framing device.

The working title should not be confused with the later commercial titles Prince of Persia: The Two Thrones or Prince of Persia (2008). “Assassins” described the early concept, while the released franchise adopted the singular brand name Assassin's Creed.