US has always been the defined of it..Fighter 'generations' have become meaningless qualifiers, used for marketing teams to try to convince people 'ours is better than the competitor's'.
You do know that they have been testing it right?They already put it into production without having even a test flight? And I thought the Soviets were terrible with pushing designs that had not been sufficiently tested into production.
Jokes aside, this the first of six prototypes. There will be extensive testing and aircraft will enter production once most of the encountered problems are dealt with.