On July 5th, Minister Wakamiya Kenji had a press conference and announced that there are 6 countries and one international organization newly confirmed their participation in the Expo; United Republic of Tanzania, Czech Republic, Republic of Trinidad and Tobago, Republic of Palau, Belize, Montenegro, and the United Nations.
This makes in total of 126 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