"As of April 15, 2013 Bethesda Game Studios made the following announcement on their blog ([1]) regarding moving on from Skyrim development and support:

"For the last year and a half we’ve been working on new content for Skyrim; from the game updates, Creation Kit, Steam Workshop, Kinect support, to DLCs. Parts of our team have also been in pre-production on our next major project, and that game is at the point where it requires the studio’s full attention to make it our biggest and best work yet."

On April 16th, 2013, Bethesda Softworks posted a cryptic video on their twitter feed ([2]) featuring classical music and barbed wire. This led many to speculate that Fallout 4 was the next major project for Bethesda Game Studios because Bethesda Softworks and Bethesda Game Studios had worked together as publisher and developer for Fallout 3 respectively. Pursuant to those rumors Pete Hines, Bethesda Softworks VP of PR and Marketing, tweeted "guess again." ([3])

On April 19th, 2013 Bethesda Softworks announced that the video was a teaser for the Evil Within. This has subsequently led to the misconception that Fallout 4 is not in the works. While Bethesda Softworks is working on the evil within, Bethesda Game Studios is not. According to the Bethesda Blog post ([4]) of April 19th, 2013 Tango Gameworks is the developer, not Bethesda Game Studios.

This means that Bethesda Game Studios has moved its full attention on to another project, but that project is not The Evil Within. Further, since their founding in 2001 Bethesda Game Studios ([5]) has only worked on the Elder Scrolls series, IHRA Professional Drag Racing and Fallout 3 it stands to reason that it is highly likely that Bethesda Game Studios has moved its full attention to Fallout 4. Unless of course they are attempting to revive IHRA Professional Drag Racing."

This was a post that I proposed to Jspoelstra and Agent c today. They wisely pointed out that it is too long and wordy for a wiki article, but I think that what I've put into it tells the complete story and creates a strong compelling argument for why Bethesda Game Studios is likely working on Fallout 4. Keep up the hope friends - Fallout 4 is coming!