Josh Gerstein reports that the Justice Department and an attorney for Assange did not immediately respond to emails seeking comment and that there are reasons to doubt that a sealed indictment actually exists:
For one thing, military prosecutors suggested in court filings in December that Assange faced no charges in the U.S. at that time. The statements came in response to motions from Assange and WikiLeaks asking that his lawyers be guaranteed access to both open and closed proceedings in the case against Army Pfc. Bradley Manning, who faces a court martial for allegedly providing hundreds of thousands of secret military reports and diplomatic cables to WikiLeaks.
In addition, the grand jury seems to have been most active in the middle of last year, which makes an indictment that would have been returned six months or so earlier unlikely but not impossible.