Check it again they have only restrictred 250CC to be 4 stroke, the 125CC is still 2 Stroke with age restrictions of 26-28 I beleive.
The 125cc class use a two-stroke engine and the last 2 use four-stroke engines. In 2010 the 250cc was replaced by the new Moto2 600cc four-stroke class.
Here is the link for it:
Wapedia - Wiki: Grand Prix motorcycle racing
Here is the pic of the recent KTM 125 CC (2 stroke)
According to KTM’s CEO Stefan Pierer, the company will continue to work on quieter, more powerful and less polluting two-strokes which would be lighter and easier to work on compared to four-stroke engines. ‘At KTM, the two-stroke will continue to remain an integral part of the future model planning,’