John Wick: Chapter 4 tactical weapons trainer and designer Taran Butler has explained how Keanu Reeves’ wild new pistol was invented specifically for the action movie. Reeves’ titular character uses a variety of weapons in the John Wick movies, including a multitude of shotguns, knives, and pistols. One pistol in particular is the Pit Viper, which is given to him by the Bowery King prior to the final action sequence of the movie. He ends up using it during the giant final battle, becoming one of his main weapons.

https://screenrant.com/john-wick-chapter-4-new-pistol-design-creation-explained/