However, the fighter continues to struggle with questions over cost and engine performance. In particular, the engines adopted for early aircraft do not provide sufficient thrust for the airframe, leaving the aircraft at a significant disadvantage compared to American fighters.
In part because of this, and in part because of Russia’s economic difficulties, the initial order has dropped to 12 (with more expected after the resolution of engine problems).
China has pushed the J-20 stealth fighter project to a stage competitive with the PAK FA
It remains unclear whether India will ever acquire a version of the PAK FA, or instead focus on indigenously developed aircraft (the distant AMCA project, which may result in a usable combat aircraft by 2030).
The PAK FA program costs about $10 billion and unit costs are about $50 million each. There would also be the operational and maintenance costs. Even at 50% of the unit cost of the F-35 and ten times few PAK-FA could cost $100 billion over four decades.