The announcement states that:
The new Japanese tech tree will initially have two branches, with a total of nine medium and five light tanks. Models will include the fabled Chi-Ri prototype, the first Japanese post-war design Type 61, the light Type 95 Ha-Go and the medium variants of the Chi-Ha. The Tier X medium tank will be the prototype of the ST-B, which was developed in the late 1950s.
The new faction is to be added via an upcoming patch, though the exact date is currently unknown.