After 25 years, any remaining debt will be discharged (forgiven). Under current law, the amount of debt discharged is treated as taxable income, so you will have to pay income taxes 25 years from now on the amount discharged that year. But the savings can be significant for students who wish to pursue careers in public service. And because you will be paying the tax so long from now, the net present value of the tax you will have to pay is small.

A new public service loan forgiveness program will discharge the remaining debt after 10 years of full-time employment in public service. Unlike the 25-year forgiveness, the 10-year forgiveness is tax-free due to a 2008 IRS ruling. The borrower must have made 120 payments as part of the Direct Loan program in order to obtain this benefit.

Unpaid Interest

In addition to discharging the remaining balance at the end of 25 years (10 years for public service), the IBR program also includes a limited subsidized interest benefit. If your payments don’t cover the interest that accrues, the government pays or waives the unpaid interest (the difference between your monthly payment and the interest that accrued) on subsidized Stafford loans for the first three years of income-based repayment.

https://finaid.org/loans/ibr/