[pietrosiorpaes]

I am an Italian citizen, and I am in the US on a F1 visa, as I am a PHD student.
I receive most of my funding through TAing, and some of if (in the summer months) from research grants.

Am I exempt from paying federal taxes in the US thanks to the tax treaty between Italy and the US (for my first two years here)?
If so, is it thanks to article 20 (professors and teachers) or article 21 (students and trainees)?

I think article 20 applies to me because I teach, and I know people in my same position who went to h&r block specialists and were told to use that article (and they did get the money back indeed).

However I am not sure, both because:
1) article 20 says it applies to "an individual who visits that State (the "host State") for a period that is not expected to exceed two years" (does this mean that I cannot apply the treaty for my first two years here, because I am expected to stay here for longer than two years?)
2) It seems to me that I am a student after all.
If I am in this category, than article 21 says :"The host-country exemption in the Article applies only to payments [... ] that arise outside the host State" and so it looks like I cannot use it (all my income comes from an American university).

Finally, does the money that I get qualify as "fellowship/scholarship", and if so it is (partially) exempt from federal taxes?

[MukatA]

F-1 visa is for students so only the article 21 applies in your case and applies for 5 years on F-1.
For article 20, you must have J-1 visa for Researcher. Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents

If you are a degree candidate and if the financial aid (includes scholarship and fellowship) is for tuition fee, other fees, books, supplies and equipment, then it is not taxable. For a degree candidate aid for boarding and travel are taxable. Scholarship and fellowship grants, Your U.S. Tax Return: The U.S. Income Tax Topics 1