It is a Federal benefit.

The Thrift Savings Plan (TSP) is a tax-deferred retirement savings and investment plan that offers Federal employees the same type of savings and tax benefits that many private corporations offer their employees under 401(k) plans. By participating in the TSP, Federal employees have the opportunity to save part of their income for retirement, receive matching agency contributions, and reduce their current taxes.

From <https://www.opm.gov/retirement-services/my-annuity-and-benefits/thrift-savings-plan/>