The four are from Yemen and had been held at Guantanamo for more than 14 years. They were suspected of being low-level militants with ties to al Qaeda but never charged.
The Pentagon announced their release Thursday following an extensive security review.
They are being sent to Saudi Arabia for resettlement and are expected to take part in a rehabilitation program.
The four include Mohammed Ali Abdullah Bwazir. He refused to leave Guantanamo in January 2016 as two other prisoners were being resettled in the Balkans.
The prison’s population is now 35, with 19 cleared for release.