https://www.theverge.com/2018/12/4/18124479/pokemon-go-niantic-trainer-battles-pvp-new-features-release-date

The next chapter for Niantic’s Pokémon Go involves borrowing another popular element from the game series’s main installments: battling. The new trainer battles feature has been a long time coming. It was first teased with the game’s announcement more than three years ago, and it’s taken the company quite a while to get it in working shape. Niantic released some new details about the feature last week on Twitter, but at a recent press event in San Francisco, the developer broke down exactly how the new battle system will work when it launches globally later this month.

Essentially, trainer battles will be quick, roughly four-minute bouts between you and another player using three pokémon each, with the opportunity to switch between the three mid-battle. A short timer determines how often you can rotate those fighters. The other big factor will be the new leagues, with the choice between the great, ultra, or master leagues that determine how powerful the creatures you use can be, which are measured by the combat power (CP) rating.