Not sure if it's true but....
According to KeyPublishing guys:
Long-term plan for the T-50 to 2020 :
2016 - T-50-9, T-50-10, T-50-11.
2017 - T-50-12 (static), T-50S-1,2.
2018 - T-50S-3,4
2019 - T-50S-5,6,7,8, PMI 1,2.
2020 - T-50S-9,10,11,12, PMI 3,4.
Which in turn was taken from a Russian...