Hi,
I am from Germany, on a F1 (PhD) at an US University and about to file my first tax return. Germnay has a treaty that goes for 4 years. I don't know yet how long I will be staying, 3 1/2 years is the plan, but it might get to be over 4 years.
So should I not claim the treaty benefit from the beginning?
And if I claim the treaty and stay over 4 years, how would the retroactive payment work?
Would I have to pay it all back at once?
Another question is what if I come back to the US to work (on a different visa). Would I than also have to pay back the taxes once I'm in the US more than 4 years?

I would be grateful for any thoughts on this!

The IRS website also says about the Germany-US treaty for students:
"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."
Who exactly are these "competent authorities" and what would be necessary to ask them (paperwork? )? And what would be necessary to convince them to "agree otherwise" ?