Other than evolving the Pokemon by collecting candies and acquiring certain special objects, there will be a new way for players to evolve some of the Pokemon in Pokemon Go now.
Just like in the normal game, players can evolve some of the Pokemons by trading and this mechanic has now added to the game as well. When plater gets an eligible Pokemon through a trade, the Candy requirement will be taken out for players can evolve it for free.
While the feature is new, the feature will also be applied to Pokemons that you have traded in the past as well so do remember to check on the other traded Pokemons to see you any of them are eligible for the free evolve.
The Pokemon that will be eligible include Kadabra, Machoke, Graeler, Alolan Graveler, Haunter, Boldore, Gurdurr, Karrablast, and Shelmet.