From GameWatcher: “Assassin’s Creed Odyssey is really full of surprises, it seems, as the latest in a long line of wonderfully amusing easter eggs is a hint that Splinter Cell and Assassin’s Creed are set in the very same universe. More importantly, it’s a hint that a new Splinter Cell game may be announced soon enough!”
Source: N4G PC Splinter Cell Exists in Assassin's Creed