On April 8th 2022, Mr. Wakamiya Kenji, Minister for the World Expo 2025, had a press conference and announced that there are 13 Countries and regions and one international organization newly confirmed their participation in the Expo; Antigua and Barbuda, Republic of El Salvador, Republic of Guyana, Republic of Cote d'Ivoire, Democratic Republic of Sao Tome and Principe, Saint Christopher and Nevis, Tuvalu, Republic of Togo, Republic of Vanuatu, Republic of Benin, Plurinational State of Bolivia, Republic of the Marshall Islands, Palestine, and PIF Secretariat.
This makes in total of 100 countries and regions and 7 international organizations that have confirmed their participation, as of April 8th 2022.
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