As we at Radio Free Skaro first discussed earlier this year, Matthew Graham has indeed been confirmed as a writer for Series 6. Doctor Who Magazine 428 reports that Graham will be penning episodes 5 & 6, which comprise a two-part story.
On a (likely) related note, Doctor Who Spoilers is reporting the casting of Sarah Smart for an upcoming two-parter to be directed by Julian Simpson. The first filming block comprising episodes 3 & 4 has wrapped and the current filming block comprising Episodes 1 & 2 is underway, and currently filming in America, so we anticipate episodes 5 & 6 to comprise the next filming block. (UPDATE: Graham has himself confirmed this on Twitter.)
Graham, whose previous Doctor Who credit is 2006′s Fear Her has also had great success with Life on Mars and Ashes to Ashes. While Fear Her may not be a lauded classic for most, having Graham on the Series 6 writing team definitely excites the Three Who Rule!