Congress enacted the First Step Act in 2018 to combat the huge prison sentences mandated by certain drug offenses. The law allows qualifying individuals to apply to district courts for modifications of their sentences. The U.S. Supreme Court is considering whether lower courts "must"—or "may"—consider intervening developments when adjudicating a request for a modified sentence.

Carlos Concepcion pleaded guilty in 2008 to a drug offense, and the district court sentenced Concepcion as a career offender. In 2019, Concepcion sought resentencing under the First Step Act, which made retroactive certain changes to mandatory-minimum sentences of drug offenses. Concepcion also contended that, since his sentencing, the law had changed concerning his status as a career offender. He asked the district court to consider this change, as well as his post-sentencing rehabilitation while in prison, in imposing a modified sentence.