The most recent episode of the Pokémon anime has confirmed what anyone with a lick of sense should have known already - that Ash's Pikachu did not evolve into Raichu, despite misleading previews and leaks.
In the Pokémon video games, it's usually advisable to evolve a Pokémon to its highest form as soon as possible. Ash Ketchum isn't quite as discerning in the Pokémon anime, and he will often use a team filled with base and mid-form Pokémon. Pikachu is the longest-running example of this, as it has yet to evolve into a Raichu, despite several episodes toying with the prospect over the years.
A recent leak suggested that Ash's Pikachu was going to evolve into a Raichu in the latest episode of Pokémon Journeys: The Series. The leak claimed that an outbreak of Pikachu would happen and both Ash and Goh go to see them. According to the leak, Ash's Pikachu was convinced to evolve by a female Pikachu, leading to him touching a Thunderstone and evolving into a Raichu.
The latest episode of the Pokémon anime has now been broadcast in Japan and it turns out that all of the hints were misleading. It turns out that Goh caught a Pikachu and that turned into a Raichu instead. Goh now has a Raichu on his team and Ash's Pikachu remains in its regular form.
The idea of the Pokémon anime changing its mascot after all of this time was laughable and there was zero percent chance of it happening, barring an introduction for a method of undoing the evolution that is used at the end of the episode. There is also the question of whether Ash's Pikachu can evolve in the first place, as he has a Gigantamax form, and in the Pokémon video games, an Eevee, Pikachu, or Meowth with a Gigantamax form cannot evolve. It seems that Ash's Pikachu is here to stay, but at least a Raichu will be part of the anime for a little while as one of Goh's companions.