The Gen 7 buff is a stat change affecting certain Pokémon from Generations I through V and increasing their stats significantly in order to make them more competitive. The change occurred with the release of Pokémon Sun and Moon. You can see the whole list of updated stats on Serebii.

Summary

For the second time since Gold & Silver introduced the Special Defense stat, multiple Pokémon have had changes to their initial base stats. These changes are relatively minor, just focusing on a slight increase in one stat. However, these changes do change the way the Pokémon is to be utilised in battle.

In Pokémon GO, this buff will be reflected as a CP adjustment. Currently, Pokémon GO is using Generation 6 stats, not Generation 7 stats, so this buff is not yet active.

Here’s how stats and Max CP will look like after the Gen 7 buff is applied:

Pokémon GO stats with Gen 7 buff applied
Pokemon Gen Attack Defense Stamina Old CP New CP (Gen 7)
Arbok 1 185 158 120 1,737 1,908
Dugtrio 1 205 147 70 1,333 1,612
Farfetch’d 1 167 118 104 1,092 1,430
Dodrio 1 223 148 120 2,138 2,205
Electrode 1 176 182 120 1,900 1,945
Exeggutor 1 233 161 190 2,916 2,945
Noctowl 2 161 179 200 2,040 2,245
Ariados 2 161 130 140 1,636 1,700
Qwilfish 2 184 166 130 1,910 2,013
Magcargo 2 155 209 120 1,543 1,857
Corsola 2 118 175 130 1,214 1,378
Mantine 2 148 260 170 2,032 2,310