— Pokémon GO (@PokemonGoApp) December 26, 2018
According to the announcement, Trainers will be able to earn double XP when they catch Pokémon, as part of an effort to help them reach a higher Trainer level before the new year. The double XP will run from December 26 to December 30.
Then, from December 30 to January 2, Incubators will be twice as effective. Additionally, Trainers can still earn a free, single-use Incubator once per day by spinning a Photo Disc on a PokéStop until January 2.
This will be the conclusion of a two-week schedule that saw other boosts including double Catch Stardust and double Candy. The next major event will take place on January 12 with Community Day, where trainers will have 3 hours to catch as many Gen. 2 Pokémon as possible.