They have external hardpoints and the engines are in external nacelles; not enclosed in the airframe.
Shhhh! Don’t tell them!...............
Exposed engines/outlets (hard IR sources), and no thrust vectoring. The Russians have been good in the past with aerodynamics, but . . .
Just because the Russians advertise them as stealthy, or Gen 5, does not make it so. The Russians will sacrifice stealth for speed & agility. We will sacrifice speed & agility to get the first-look/first-shot. Who is right?