This didn't get much traction in the news a couple of weeks ago but is part of what AG Holder has been working on to reduce the prison population. This is expected to reduce the population by about 6500 in the first 5 years.  They are still constrained by mandatory 5 years sentences. This just shows how a unified effort is behind this. I am sure Harry Reed will not bring it up to a vote. 

The U.S. Sentencing Commission voted Thursday to reduce sentencing guidelines that could shorten prison stays for about 70% of federal drug trafficking defendants, backing a proposal supported by the Justice Department and some conservative lawmakers.

The unanimous vote by the commission sets in motion a change in the formula used to determine sentences for federal drug offenders. If Congress doesn't object to the change, it would go into effect on November 1.

"This modest reduction in drug penalties is an important step toward reducing the problem of prison overcrowding at the federal level in a proportionate and fair manner," said Judge Patti B. Saris, chair of the commission. "Reducing the federal prison population has become urgent, with that population almost three times where it was in 1991."