Microsoft has a couple of unannounced first-party studios working on exclusives, recently promoted Head of Xbox Phil Spencer has said.

Spencer said on Twitter that he still believes that exclusive content is a key to console success, and that Microsoft expands its lineup of first-party studios when it has a great idea to build. “We’ve been doing this with a few things lately,” he said.

New Microsoft first-party studios that are developing games for the Xbox One include Team Dakota, currently at work on Project Spark, and Black Tusk Studios, which has taken over the Gears of War franchise Microsoft acquired in January.

Spencer also mentioned Lift London, another first party developer that we last heard was working on four, free-to-play titles for "connected platforms.” Spencer added that there are also “a couple” of unannounced studios.

He previously said that Microsoft’s 90-minute E3 presentation will focus on games, so we might find out who these studios are and what they’re working on then. E3 2014 runs June 10-12 in Los Angeles.