Oklahoma voters' approval of a referendum in 2016 allowed for nearly 500 inmates to walk free on Monday from the state's massive prison system—the largest single-day commutation in U.S. history.

Four hundred and sixty-two people had their sentences commuted as a result of Question 780, which asked voters if they approved of recategorizing many felonies, including drug possession and minor property crimes, as misdemeanors. The referendum passed by a 16 percent margin.

This year, state lawmakers also made the new law retroactive and allowed parole boards to quickly review many inmates' cases. A total of 527 sentences were commuted; 65 people will also be released early at a later date.

Kristen Clarke, executive director of the Lawyers' Committee for Civil Rights Under Law, called the historic commutation on Monday a "step forward in the fight to end mass incarceration."

Oklahoma is the incarceration capital of the world. Today appx 527 inmates will be released after a state panel approved the largest-ever single day US mass commutation. This is one step forward in the fight to end mass incarceration. #cjreform https://t.co/le2mtSVfvF — Kristen Clarke 866-OUR-VOTE (@KristenClarkeJD) November 4, 2019

Ryan Kiesel, executive director of the ACLU in Oklahoma, noted the significance of Oklahoma voters' call for reforms to the criminal justice system.

"From the 30,000-foot view, the criminal justice landscape is light-years ahead of where it was three or four years ago," Kiesel told the Washington Post. "It would have been impossible before State Question 780 passed in Oklahoma; that signaled to lawmakers there was an appetite for reform."

German Lopez, a journalist at Vox, wrote that the fact that there appears to be little outcry over the release of nearly 500 inmates "is probably good—a sign of how far criminal justice reform has come."

That this is largely flying under the radar is probably good — a sign of how far criminal justice reform has come. https://t.co/pcAzfKtJna — German Lopez (@germanrlopez) November 4, 2019

In addition to the crime reclassifications, the state is offering new resources to inmates to assist them with re-entry into society following their sentences. Former prisoners will be given a state-issued ID to help them secure housing and work, and will be connected with housing and counseling services.

Udi Ofer, director of the ACLU's justice division, emphasized that with more than 26,000 Oklahomans still living in the state's prison system, more work needs to be done regarding sentencing laws.

"Oklahoma will never substantially reduce its prison population until it tackles sentencing enhancements," Ofer told the New York Times.

Legislators are currently weighing reforms that end long sentences for repeat offenders convicted of nonviolent crimes, shorten drug sentences, and limit the use of cash bail.

The state's Pardon and Parole Board is expected to commute sentences for nearly 1,000 people as a result of the law making the referendum retroactive. More than 800 people applied for commutation on Friday, when the new law went into effect.