Niantic yesterday published the details of the next Pokemon GO update.
The update going to change the training and the battles in the friendly Gyms where you can now fight with 6 pokemons instead of only 1.
“As we continue to make improvements to Pokémon GO, we have made an enhancement to the Gym experience for Trainers of all levels. In an upcoming version of Pokémon GO, when training at a friendly Gym, Trainers will be able to bring six Pokémon to battle instead of one. In addition, the CP of the Pokémon you are training against may be temporarily adjusted lower during your training session to generally match your Pokémon’s battle capabilities.
No matter what your level, you can now have an impact on your team’s Gym. Walk with your Buddy Pokémon to that nearby landmark and show your Team Leader that you can battle with the best!”