...The Commission’s actions today, as well as promulgation of the original amendment for crack cocaine offenses, are only a partial step in mitigating the unwarranted sentencing disparity that exists between Federal powder and crack cocaine defendants. The Commission has continued to call on Congress to address the issue of the 100-to-1 statutory ratio that drives Federal cocaine sentencing policy. Only Congress can provide a comprehensive solution to a fundamental unfairness in Federal sentencing policy. The Commission has consistently expressed its readiness and willingness to work with Congress and others in the criminal justice community to address this very important issue.

Other statements on the decision: FAMM.

More on this here.

(c) Modification of an Imposed Term of Imprisonment.— The court may not modify a term of imprisonment once it has been imposed except that— ....(2) in the case of a defendant who has been sentenced to a term of imprisonment based on a sentencing range that has subsequently been lowered by the Sentencing Commission pursuant to 28 U.S.C. 994 (o), upon motion of the defendant or the Director of the Bureau of Prisons, or on its own motion, the court may reduce the term of imprisonment, after considering the factors set forth in section 3553 (a) to the extent that they are applicable, if such a reduction is consistent with applicable policy statements issued by the Sentencing Commission.

Update: New York Times report.