Interplay is getting help from Bulgarian developer Masthead Studios who will be joining them to work on the publisher’s mysterious MMO codenamed Project V13, which is rumored to be a Fallout MMO.

The agreement sees Masthead co-developing the game with Interplay’s internal teams under their direction and control. It will also see Masthead implementing tools and technology created for Earthrise – a post-apocalyptic MMO due out later this year.

Interplay is yet to announce any solid details on Project V13, though it is known that Jason Anderson – one of the original Fallout’s original designers – had been working on the project before he left to work for inXile.