Bayek uses the Hidden Blade in Assassin's Creed Origins.
The Hidden Blade is a retractable wrist weapon associated with the Assassin tradition. In Origins, Bayek receives one from Aya and uses it during the game's story in Ptolemaic Egypt. Its first use causes a memorable injury because Bayek has not yet adapted to the weapon's mechanism.
Origins is set in the first century BCE and presents the formation of the Hidden Ones, the organization that later develops into the Assassin Brotherhood. The game therefore gives the weapon an early place in the franchise's fictional history without claiming that it was invented in the modern era.
The Phantom Blade is a ranged wrist-mounted weapon introduced in Assassin's Creed Unity. Other games include poisoned blades and upgraded wrist weapons, but the standard name for Bayek's signature concealed wrist weapon is Hidden Blade.