The official twitter account of One Piece announced that Saori Hayami will play the role of Yamato on the said anime series.

【超速報】

ーーーーーーー
ヤマトのキャストは#早見沙織 さん!
ーーーーーーー

ご本人のコメント映像を御覧ください！

↓YouTubeでみる↓https://t.co/8W9LA2OHOW

ヤマトは9月5日のTVアニメ本編に先駆けて、先程公開の"#WeAreONE."第２話に登場！

↓第２話↓https://t.co/vSlX7ESKmS pic.twitter.com/LT5AFhTdg1

— ONE PIECEスタッフ【公式】 (@Eiichiro_Staff) August 30, 2021

On the said announcement, Yamato will appear on the episode 990 on one of the longest running shounen anime in Japan. Episode 990 will broadcast this September 5.

Yamato also appeared in the video “ONE PIECE Vol.100 / Ep.1000 Celebration Movies” WE ARE ONE.” which was released last August 31 prior to the 990th episode of the said anime.

Source: Dengeki Online