2. IRA withdrawals by a US Person resident and taxable in Switzerland will be taxed by the Swiss and the IRS. A foreign tax credit for taxes paid to Switzerland should be filed with the IRS for at least partial tax relief.
For more information:
https://www.irs.gov/pub/irs-trty/swiss.pdf
One is only taxable on pension income allocated from given state. So assume that your SS payments will only be taxable in the US.
The US-Swiss Tax Treaty has a so-called "Saving Clause" at Article 1, Para. 2.:
"ARTICLE 1
Personal Scope
2 Notwithstanding any provision of this Convention except paragraph 3 of this Article, the United States may tax a person who is treated as a resident under its taxation laws (except where such person is determined to be a resident of Switzerland under the provisions of paragraphs 3 or
4 of Article 4 (Resident)) and its citizens (including its former citizens) as if this Convention had not come into effect."
In plain English, a Saving Clause says that the U.S. has the right to tax its citizens abroad as it so decides but may relax this double taxation in selected areas.
Regarding US social security paid to US Persons in Switzerland, an excerpt from the below linked document notes:
"U.S. Social Security Benefits paid to Swiss residents
The United States, as the source country, subjects up to 85 percent of the benefits paid to U.S. citizens residing in Switzerland to taxation. Switzerland, as the residence country, also subjects the U.S. benefits received by those individuals to taxation. Foreign tax credit relief can be applied only on the U.S. side."
OP, the new treaty now recognizes IRAs as if they were Pillar 3 accounts and vice versa. The same is not true for Pillar 2 accounts and US Pensions. Any distributions will be taxable in Switzerland as income. Against this, you will be able to claim the foreign tax credit and possibly credits for any taxes paid on the post-tax contributions to your IRA (if structured as a Roth). However, you will need expert help with this and should contact an accountant as soon as possible to understand all the ramifications of your specific situation. This expertise could save you lots of money.