If you had a co-borrower from the start, paying the loan off would not be a gift because they were a borrower. However, if you are the only borrower and someone wants to help you pay off the loan, I think adding them as a co-signer would be viewed as a "fig leaf" to disguise what is really happening, and the IRS doesn't do fig leaves. If it's a gift, it's a gift. However, as mentioned, even though a gift tax return may be needed, payment of gift tax is very rarely required.
