Here’s a statement from the Swiss Federal Council on the TPNW:

On the basis of a new comprehensive reassessment, the Federal Council decided at its meeting on 27 March 2024, that there is currently no reason to change its position on the Treaty on the Prohibition of Nuclear Weapons (TPNW), which entered into force in 2021. It has therefore reaffirmed the conclusion it reached in 2018 and 2019 and has decided that Switzerland will not join the TPNW for the time being. The Federal Council’s conclusion is based both on the assessment made in 2018–19 and recent security policy developments in Europe and globally. The Federal Council considers Switzerland’s commitment to a world without nuclear weapons, pursued within the framework of the Nuclear Non-Proliferation Treaty (NPT), to be a more effective approach.