Xbox One’s Halo title is indeed a “legitimate” entry in the series, according Microsoft game studios VP Phil Spencer, he also said that the Halo series is now saga, instead of a seperate series. Speaking with GameSpot during E3, Spencer didn't specify whether the new Xbox One title will be Halo 5, or another game that contains a different subtitle. The firm will talk more about the story arc and “how it plays out” at another time.
“Having [producer Bonnie Ross] come out [at E3] and announce the game, making sure people know it’s a legitimate version of Halo coming out, and when it’s coming out, and features that they’re focused on we thought was…important,” Spencer said.
Halo 4 was supposedly the start of a new trilogy, but the company has a new take on the long running sci-fi shooter. “While we originally said trilogy, we’ve actually expanded this to more of a saga, so we don’t want to limit the Reclaimer story within a trilogy,” said the company.
