On June 7th, Minister Wakamiya Kenji had a press conference and announced that there are 4 countries newly confirmed their participation in the Expo; Kingdom of the Netherlands, Republic of Poland, Federal Democratic Republic of Ethiopia, and Niue.
This makes in total of 119countries/ regions and 7 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