I did not read every word of this article, but it looks good.
«The Su-57 is a high maneuverability air superiority fighter, with a substantially reduced radar cross section compared to 4th generation Russian fighters, designed to work as part of Russian air defense to counter stealth aircraft near or within Russian airspace. This fighter is meant to team with Russia’s sizable 4th gen air force, and VHF/UHF ground based acquisition radars, to establish local qualitative advantages and help close corridors in Russian air defenses. The Su-57 is an affordable, producible option to bolster Russia’s air defense network. It will pose a major challenge for any 4th gen aircraft, and concern to stealth optimized 5th gen aviation. Yes it is a stealth 5th generation aircraft, but it is not a F-22 or F-35 clone, and the design philosophy is not based around mission requirements similar to U.S 5th generation aircraft. This fighter is tailored to Russian needs, though it has features intended to make it attractive to an export market.»