Russia is cancelling the Su-57 (aka T-50) stealth fighter. They built 11 planes in early production but India has dropped out as a partner. Russia will apply the stealth technology and other advancements for an improved version of the SU-35.
Russia flew the plane in Syria but it had engine troubles and the stealth is inferior.
Most of the first five prototypes developed severe structural problems, engine breakdowns and cockpit glazing problems. India had agreed to co-finance the T-50, but dropped out because the T-50’s engines were unreliable, inadequate radar and badly engineered stealth.
The SU-37 had significant problems flying and releasing bombs at supersonic speeds.