Rainbow Six Siege's leakage problems are a thing of legend already but it wasn't data miners or people with insider connections that revealed Y5S1 operator's weapon - Ubisoft leaked it themselves on the test server (PTS).
Leaks for upcoming video games and video game updates are a disheartening thing for developers in some cases, as evidenced by Jeff Kaplan's recent statements, but it's hard to gauge whether Ubisoft are unable to stop Rainbow Six Siege leaks or they encourage them in order to keep the hype going.
The new operators, Kali and Wamai, have barely debuted on PTS and are yet to see the light of day on live servers but it's already known that a Year 5 Season 1 (Y5S1) operator will have the SPAS 12 shotgun in their loadout.
As weird as this may sound, the leak was technically not done by a third party but by Ubisoft themselves. One player received a skin for SPAS 12 which is already in the game, in use by Valkyrie. When a player gets a weapon skin in Rainbow Six Siege, there is a small indicator that lists the operators that can use it.
Such was the case with the SPAS 12, as the game was supposed to list the only user of the shotgun so far, Valkyrie, but next to it. There is no image of this upcoming operator, only the text that says "Not ready for testing", "Def" and "Y5S1".
That is still plenty of info though. Now we know it will be another defender with SPAS 12, long before the operator comes out. In fact, we got the info even before Kali and Wamai came out, since both of them are still in the testing phase.