(These are the more common agreeable things I could find, I am no expert in this specific topic and there are things that I could be very wrong about. If you doubt this info, I highly advise you to do your own research to get your own conclusions.)
What’s commonly defines a generation for MBT’s.
Generation 1
Gen 1 are defined being the first “Universal Tanks”, Tanks that are matching or even outmatching the heavy tanks in protection and firepower, allowing them to be used more effectively in mutliple roles.
First generation tanks are primarily medium tanks and later changed into main battle tanks through changes in doctrine.
The first generation tanks include
Centurion
T-54
M48 Patton
Fv4202
T-55
Type-59
Type-61
(Other tanks at the time that could be given the designation too, but weren’t due to their medium tank designation.)
Spoiler
M26 Pershing
Pz.V Panther
T-44
2nd generation
The second generation of MBT marked a turn in the doctrine. This generation was also marked by the utilisation of Night vision, new advanced ammunition such as the APDS, HEAT, HESH and later the APFSDS.
The second generation tanks include
M60
T-62
Leopard 1
Panzer 61
MBT-70
Vickers MBT Mk.I
AMX-30
T-64
FV 4201 Chieftain
Magach 3
Strv 103
WZ 122
Panzer 68
Type-69
T-72
Type-79
Olifant Mk.1/Mk.2
Type-74
Magach 5
Vickers MBT Mk.3
Shir 2
Merkava Mk.I / Mk.II
Type-80
Type-86
Type-96
OF-40
MB-3 Tamoyo
3rd Generation
The third generation of main battle tanks is characterized by composite armour and computer-stabilized fire control systems, which allow firing on the move as well as very high first hit probability on targets multiple kilometres away. Most of those tanks had calibers larger than 105mm.
The list of 3rd gen tanks are
M1 / M1A1 / M1A2 Abrams
Leopard 2
T-80
T-84
Challenger 1
AMX-40
M-84
K1 / K1A1
Merkava Mk.III
Type-90 / Type-90 T-ReC
Leclerc
T-90A
T-72M2 Moderna
PT-91 Twardy
Ariete
Challenger 2
ZTZ-96A / B
ZTZ-99
MBT-2000
Arjun Mk.1
Sabra M60
M60A3 SLEP
Generation 3.5
An intermediate generation of third-generation tanks modernized with newer hardware and software to keep themselves up to date with the everchanging modern battlefield.
These upgrades are often included (not always at once,) as for example; more advanced thermal sights (Generation 3), datalink capability, Softkill APS, hardkill APS, Laser Warning Receivers.
List of gen 3.5 tanks include
Merkava Mk.4M
Leopard 2A7+
T-84 Oplot-M
T-90M
K1A2
ZTZ-99A
VT-4
T-80BVM
T-72B-3 UBH
M1A2 SEP V2 / V3
Leopard 2 PL
Ariete AMV
Type-10
K2 Black Panther
Challenger 2 Black Knight
4th generation
The next generation of main battle tanks in development has autoloaders becoming increasingly more common, even in western designs, with some moving all of the crew into a more heavily protected hull space with unmanned turrets. The tendency to increase calibre sizes continues, with multiple designs having capability for 140mm guns to be fitted. A greater focus on active protection systems, especially against drones and loitering munition is also present, as is the introduction of AI-assisted systems.
4th generation list of tanks include
T-14 Armata
Leclerc XLR
Challenger 3
Type 100
KF-51
Abrams X
M1E3 Abrams
Leopard 2A8