The official Pokénchi website posted this news article announcing the 20th anniversary special on March 15th, 2017.

On Saturday April 1st 2017, it will be the exact 20th birthday of the "Pocket Monsters" anime, which started airing April 1st 1997. At the house where Pokémon fans gather, "Pokénchi", both the Pokénchi residents and guests that truly love Pokémon will gather to celebrate that the Pokémon anime is now 20 years old!!

We will bring you tons of precious and nostalgic clips from TV series and movies featuring famous touching scenes and famous Pokémon battles that won't fail to excite you! Not only that, but Abareru-kun and Shokotan will leave Pokénchi to visit a company that produces Pokémon toys, as well as "other Pokénchi"! And you can't miss the special live concert with Rica Matsumoto, the voice of Satoshi! To celebrate this memorable day, just say "I Choose You" to this special program!!

Title: The Exact 20th Anniversary for the Pokémon Anime "Pokémon no Uchi Atsumaru?" Special

Air date and time: Saturday April 1st at 4pm to 5:15pm

Cast: Shoko Nakagawa, Hyadain, Abareru-kun, Rinka Otani, Rica Matsumoto, Koichi Yamadera, Hiroshi Yamamoto (from Robert), Louis Kurihara, Tomohisa Sako, Nemu Yumemi and Eimi Naruse (from Dempagumi Inc.), Toshiaki Kasuga (from Audrey), Miyu Koike, Seishiro and Kenshiro Kato, Director Kunihiko Yuyama and more

Source: http://www.tv-tokyo.co.jp/anime/pokenchi/news/