Since it has two turrets it will most likely be introduced when the multi-turret system is inplimented.
The in-game description was also leaked: Development of the M1921 tank began in 1919. By February 1922, the Packard Motor Company manufactured a prototype. The tank featured a number of innovations, including a commander’s cupola and peculiar tracks with wooden inserts. The vehicle was never mass-produced, but further experimental vehicles, the T1 and T1E1, were developed on its basis.
Designed in 1921 at the Rock Island Arsenal plant, it was tested at Aberdeen in February 1922. It had a British cable and suspension track design and used several engines (from 220hp Murray-Tregurtha to 338hp V12 Liberty), allowing it to go as fast as 26 km/h (16 km/h with weaker engine). It weighted 18,6 tons and was armed with a contemporary British 6pdr (57mm), along with a 30cal MG. The armor values I haven't found, but they most likely are very thin. This vehicle never got to be manufactured.