I have been in US since 2000 on F1. In 2009, I finished my PhD and started working for a company on OPT. For filing 2009 tax return, I will apply as a "resident alien for tax purposes". My question is regarding a treaty benefit between my country Pakistan and US which allowed me to claim tax exemption from first $5000 of my income every year. Can I still claim this benefit and file a form 8833 since being on OPT means that my visa status is still F1.
moody2009

If you file as a resident alien, you forfeit any treaty exemption.

Actually, this is okay, because you get to claim the $5,700 standard deduction (something you could NOT claim if you filed as a non-resident alien) instead of the $5,000 treaty exemption, so you come out ahead.

BOTTOM LINE: File as a resident alien.

I found this online:
"A foreign national who must file as a resident may nevertheless be entitled to tax treaty benefits. To claim tax treaty benefits on Form 1040, the individual must attach a completed page 5 of the Form 1040NR to the return, write "Tax treaty exemption pursuant to the tax treaty with (give the country)" at the top of page 1 of the return, and send the return to Internal Revenue Center, Philadelphia, PA."

To me it seems, I can claim the tax treaty benefit for 2009. The only problem is that I did not give a declaration to my employer about claiming tax treaty benefits. But I guess, I can deduct $5000 from my gross income before writing it on the 1040.

If you believe that you can claim the treaty benefits, there is no harm in trying, but it is my opinion that you forfeit the treaty exemptions when you begin filing as a resident alien.