In early 2016, Tim Cain & Leonard Boyarsky both began work on a secret project that at the time we only knew was being built inside Unreal Engine 4. This top secret project is now confirmed to be a multi-platform RPG as it is described in this job posting.
The mention of UE4 is a clear indication that it is connected to this secret game, and one thing worth noting – there is an emphasis on having AAA titles shipped as a requirement.
This fact and the mention of the game is a multi-platform release, a requirement for reporting to ‘stakeholders’ and the fact that this game needs a UI team of more than one person is a sign that the game is already picked up by a publisher and it will be an AAA title.
In April 2017, Tim Cain gave a talk at the Reboot Develop conference and confirmed that he was working on a new IP that has a lot of “Fallout and Arcanum style of humor.”
More evidence comes from this interview with USGamer (the important part starts at 35:42). Feargus mentions that he has been replaying Fallout: New Vegas because of this new secret game but he then said that it is not related to Fallout.
All of this should be a clear indication that Obsidian is currently working on a big new title and we should be getting more news soon.