Hi,
I am an F1 student with Indian Nationality currently on an extended OPT visa. I am a non-resident alien along with my wife who is on an F2 visa (not employed) who is also non-resident but has a ITIN.
My question is due to my nationality, am I allowed to claim 2 allowances in my W-4 form? If yes, would I need to fill out Form 8233 to prove the tax treaty exists between US and India that allows me to do so?
Yes, you can claim 2 allowances and you do not need to write "nonresident alien" on line 6.
You do not claim a tax treaty with form W4, that form is for the employer only. You would claim the treaty when you file your return. Turbotax does not support nonresident alien returns. You would need to file form 1040NR plus form 8843.