Last year I was finishing my OPT period (I had a F1 visa) and then changed my status to G4. Can I claim the $5000 deduction mentionned in the French/US Tax treaty for the income I earned as I was an F1 visa-holder ?

Yes; the $5,000 exemption carries over if you have earned at least $5,000 while you were an F-1 visa holder.

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