The Justice Department will grant early releases to about 6,000 federal inmates within weeks, the federal Bureau of Prisons confirmed Tuesday.
The inmates, all drug offenders, will be freed between October 30 and November 2, BOP spokesman Ed Ross confirmed to NBC News.
The release, which had been expected for months, is a result of the U.S. Sentencing Commission's change to sentencing guidelines for drug offenders last year.
It is the largest ever one-time release of federal prisoners, according to the Washington Post, which first reported the story.
The average sentence reduction for those who've applied for retroactive sentencing since the amendment is 23 months, lowering the average sentence from 131 months to 108 months, the Justice Department said.
Deputy Attorney General Sally Quillian Yates said they were "modest reductions" for drug offenders, who will have served "substantial prison sentences."
"The Department of Justice strongly supports sentencing reform for low-level, non-violent drug offenders," she said in a statement. "The Sentencing Commission's actions — which create modest reductions for drug offenders — is a step toward these necessary reforms."
Most of the released prisoners were already in halfway houses and home confinement, Ross said.
There are more than 205,000 people in federal prisons, according to the Bureau of Prisons. The bureau said it expects that population to decline by 12,000 inmates by the end of the 2016 financial year.
The move is separate from President Obama's push to grant clemency to some non-violent drug offenders.