that didn't take long: Russian players started spreading rumors about the upcoming tier 9 "Mammut" tank. I will post this here just in case any make it to the EU/NA server.
The first news that emerged was that that Mammut will replace the VK4502B instead of Mäuschen. Nope, Mäuschen is still the replacement. The "Mammut" is an event tank (tier 9 CW/special event/whatever). What the purpose of the game will be we might learn soon as Aleksei "Inaki" Ilyin (one of the producers) stated Wargaming might release more info today.
Interestingly enough, according to Inaki its tier is not set yet completely - it's possible that this vehicle will be either tier 8 or tier 9. Unfortunately, it's also not a replacement for the (seriously unhistorical) VK4502A.
Some videomakers (Jove) started also spreading that this tank is completely fake, made by Wargaming. Nope, it existed, you can read about it here in Thor_Hammerschlag's article.
The Mammut is most likely a CW tank as it is too early to implement tanks for next round of individual missions but it could be something new entirely.