Which one is not a Stealth Plane?

F-117 Nighthawk and B-2 Spirit are dedicated stealth aircraft designed with radar-absorbing materials and faceted shapes to minimize radar detection. SU-47 Berkut is a Russian technology demonstrator with forward-swept wings that has some reduced radar cross-section features. SU-37 is an upgraded Su-35 Flanker fighter with no stealth characteristics - it's a conventional air-superiority fighter focused on maneuverability and thrust vectoring, making it the only clear non-stealth option among the choices.