The Russian Armed Forces are working on the Mig-41, a new supersonic fighter based on the Mig-31 Foxhound.
March 5, 2014 by Jacek Siminski.

According to the famous experimental pilot Anatoliy Kvochur, the MiG-41 is to be capable of reaching speeds above Mach 4, even Mach 4,3. That would make the plane faster than the (now retired) American SR-71 Blackbird. Currently, the Foxhound is capable of flying at speeds of Mach 2.8.

Nevertheless, while developing a Mach 4+ replacement for the Foxhound, the Russians will to continue the modernization program of the Foxhounds, overhauling over 100 aircraft.

MiG-31 is an interceptor based on MiG-25 Foxbat, with a combat radius of 720 km. A group of four Foxhounds is able to control an area that is 1000km wide; 190 MiG-31s are currently in service within the Russian Air Force, 100 of those are still flyable.

http://theaviationist.com/tag/mikoyan-mig-31/

A new MiG-41 aircraft may be developed on the basis of MiG-31 fighter-interceptor

Wednesday March 5, 2014 17:20

A new MiG-41 aircraft may be developed on the basis of MiG-31 fighter-interceptor, the representative of State Duma’s Defense Committee, deputy Alexander Tarnaev, told the journalists at the Cultural Center of Russian Armed Forces, ITAR-TASS reports.

"The corresponding decision was taken by the Chief of General Staff; he has already signed the document on carrying out the research work in the network of MiG-41 project", - he noted. According to the deputy, MiG-41 “will embody all the advantages of the jet”.

In addition, a few hundreds of MiG-31s may be overhauled and put into service by the Russian air forces, Tarnaev noted. "The government decided to overhaul and put into operation MiG-31 fighter-interceptor", - he said. "This refers to hundreds of jets, which will be operated by the Russian air forces after being overhauled", - the deputy noted. MiG-31 is the two-seat supersonic long-range fighter-interceptor. It was developed by OKB-155 (currently RAC “MiG”) in 1970s.

MiG-31 is intended for interception and annihilation of air targets at low, medium and high altitudes under any lighting and weather conditions; the jet is effective against active and passive electronic radar countermeasures and heat flares. A group of four MiG-31s is able to control the airspace with a length of 800-900 km. Initially it was intended for intercepting cruise missiles and low-altitude satellites.

http://www.ruaviation.com/news/2014/3/5/2209/