Pokémon GO players are getting a boost with expanded Item Bag capacity tied to their level. Level-up rewards now include room for an additional 400 items, giving trainers more space to store Poké Balls, Berries and other essentials. The upgrade has been automatically granted based on each player’s current level, making it easier to stay stocked up for events and long adventures without constantly managing inventory space.
Source: Official Pokémon GO blog and Pokemon.com