On October 25th, Minister Okada Naoki had a press conference and announced that there are 5 countries newly confirmed their participation in the Expo; Slovak Republic, Republic of Tunisia, Republic of Panama, Republic of Malta, and Republic of South Africa.
This makes in total of 142 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