Until the end of March 2018, it WAS possible to be granted indefinite leave to remain after FOUR years under the Ankara provisions.
However, the UK Government, following an Upper Tier Tribunal decision, has now withdrawn indefinite leave in this category, and it is no longer possible to be granted ILR in this route.
The UK Government has indicated that they will be creating a new route to indefinite leave in the future for Ankara applications, but for now, people in this route will have to wait ten years under 276 B of the immigration rules.