On March 24, Minister Okada Naoki had a press conference and announced that there are 11 countries which newly announced their participation in the Expo; State of Israel, Democratic Republic of the Congo, The Republic of the Sudan, Republic of Seychelles, The Holy See, Republic of Peru, Republic of Malawi, Principality of Monaco, Republic of Moldova, Republic of Lithuania, and Republic of Liberia.
This makes in total of 153 countries/ regions and 8 international organizations that have confirmed their participation.
For the details, please check the list of participants on the website of the Ministry of Foreign Affairs.
Ministry of Foreign Affairs "Confirmed Participants for the Expo2025"
https://www.mofa.go.jp/ecm/ec/page22e_000942.html