Mikoyan PAK DP

The Mikoyan PAK DP (, ) is a Russian programme to develop a stealth interceptor aircraft/heavy fighter under development by Mikoyan to replace the Mikoyan MiG-31 in the Russian Air Force in mid-2020s or mid-2030s. It is often referenced as Mikoyan MiG 41, because its project code is izd.41, but its official designation has never been given, as Russian planes only get their official designation when they are about to enter service. According to the Russian defence analyst Vasily Kashin, the MiG-41 would be considered as a 5++ or 6th generation project.
Development.
It was argued at first that the work on the supersonic PAK DP MiG-41 interceptor was making use of the MiG-701 (Izdeliye 7.01), Mikoyan MiG-301 and Mikoyan MiG-321 projects begun in the 1990s. 
As of July 2016, not much information was available apart from the statement that such aircraft is planned for development, no official data was available concerning its capabilities. It was speculated that it could enter service by the mid-2020s or 2030s. As an interceptor, its primary mission was rumored to offset future reconnaissance aircraft currently being developed by the United States of America and China. To achieve the high speeds rumoured for the aircraft, the aircraft would need to be equipped with ramjet or turboramjet engines.
The design of the PAK DP was finalized by the end of 2019, at the same time the research work was completed. In 2020, within that research framework, the Russian Ministry of Defense selected the most promising project. Work in this area now continues in R&D and with wind tunnel models. Ilya Tarasenko, the general director of the MiG corporation, as well as the head of the Sukhoi company, said in an interview in July 2020 that the PAK DP will be created on the basis of the MiG-31's design 
According to Izvestia, the PAK DP is envisioned to become an interceptor of hypersonic missiles by carrying a multifunctional long-range interceptor missile system (MPKR DP) that will dispense several sub-missiles in order to increase the chance of intercepting hypersonic weapons. The PAK DP is also intended to carry anti-satellite missiles.
In January 2021, Rostec Corporation, the owner of Mikoyan, announced that the PAK DP had now entered the development phase, saying "Development of the next generation of interceptor fighters has already begun."
Design.
In an interview for Russia Today, the Director General of RSK MiG, Ilya Tarasenko, speculated that it would be a new construction capable of Mach number 4–4.3, equipped with an anti-missile laser, and said would be able to operate at very high altitudes and even in near space. He also stated that it could be transformed into an unmanned version later. If purchased by the Russian Air Force, he said that the first production PAK DP would be completed in 2025.
The aircraft may cruise at speeds of at least and fly at high altitudes (at levels between the stratopause and the tropopause, i.e. below 45,000 meters and above 12,000 meters) to cover the most amount of Russia's very large territory in the shortest period of time. It could use a variant of the Izdeliye 30 engines currently under development for the Su-57. It was said that the PAK DP will use some stealth technology.
An unmanned version is also under consideration.