Current jet fighters have been classified as 4th generation, 4++ generation, and so on, with 5th generation being the latest, i.e F- 22. What is the criteria for such segregation? B-2 is a stealth aircraft but considered 4th generation whereas Mig-35 is classified as 4++.
The Wikipedia Page for Fighter Generations has a relatively comprehensive list on how they derive at the "generation" of the fighter. For example, here is how the Air Force classifies them:
- 1: Jet propulsion : F-80, Me 262
- 2: Swept wings; range radar; infrared missiles : F-86, MiG-15
- 3: Supersonic, pulse radar, Beyond-visual-range missiles : Century Series, F-105, F-4, MiG-17, MiG-21
- 4: Pulse-doppler radar; high maneuverability; look-down/shoot-down missiles : F-15, F-16, Mirage 2000, MiG-29.
- 4+: High agility; sensor fusion; reduced radar signature : Eurofighter Typhoon, Su-30, F/A-18E/F, Rafale
- 4++: Active electronically scanned arrays; continued reduced signatures or “active” (waveform canceling) stealth technology, supercruise : Su-35, F-15SE
- 5: All-aspect stealth with internal weapons bays, extreme agility, full-sensor fusion, integrated avionics, some or full supercruise : F-22, F-35,
- 6: extreme stealth, morphing capability, smart skins, highly networked, extremely sensitive sensors, optionally manned, directed energy weapons.
Until we have a major leap in technology, it would seem we are capped off at 5th generation fighters for the moment.
There is no criteria because there is no such thing as an X-Generation fighter. That Fourth Generation / Fifth Generation stuff is a marketing gimmick cooked up and used by aerospace OEMs to sell hardware at defense trade shows. Nobody in the real world subscribes to this or even considers such nonsense. There are either fighters or there are targets. Nothing more, nothing less.