From the technical interpretation of the Thai/USA tax treaty, the saving clause states:
Paragraph 2 contains the traditional saving clause found in all U.S. treaties. The
Contracting States reserve their rights, except as provided in paragraph 3, to tax their residents
and citizens as provided in their internal laws, notwithstanding any provisions of the Convention
to the contrary.
That phrasing seems to mean that the USA considers its residents to have the same rights and obligations as its citizens for the entirety of the treaty.