Pokémon GO is in the process of being updated to a new version across all capable iOS and Android devices. The latest update is being rolled out to iOS and Android devices, respectively. According to patch notes from the development team at Niantic, the latest update implements various bug fixes and improvements for an overall smoother experience. A new loading screen has also been made available. Featured Pokémon include Pikachu, Fletchling, Litleo, Greninja and Ho-Oh.
Source: Official Pokémon GO support page