I am a German citizen and have been living in the US for 2 1/2 years. I came here for Grad school and stayed to work for while. The tax treaty between Germany and the US implies that I can take advantage of the treaty so a specific amount of income is exempt from taxes. But then there is this paragraph:

"Individuals described in the previous two paragraphs are also exempt from U.S.
tax on compensation for dependent personal services of up to $5,000 per year if: they are
present in the United States for not more than 4 years, and the services are performed for
the purpose of supplementing funds available otherwise for maintenance, education, or
training.
If the individual’s visit exceeds 4 years, the exemption is lost for the entire visit
unless the competent authorities of Germany and the United States agree otherwise."
(Source: www.hauswiesner.com/Tax%20Treaty%20Germany_USA_Basics.pdf)

When I stay longer than four years, apparently I will have to pay taxes on all my income I made until then. My question is whether or not there will also be interest that I have to pay on top of that.

Any answers are greatly appreciated!
Thanks!
Sonja