CBS has set a 90-minute premiere for “Big Brother” Season 27 on July 10 at 8 p.m. Eastern, returning the long-running reality franchise to prime time for its 25th anniversary year. Host Julie Chen Moonves is back to welcome 16 new contestants into a redesigned set dubbed “Hotel Mystère,” part of this season’s overarching theme, “A Summer of Mystery.” The network is also holding back one major twist: a 17th “Mystery Houseguest” whose identity will be revealed during the season. Additional curveballs include a masked visitor, a secret accomplice and the revival of last year’s AI-powered game feature, now rebranded the “BB Blockbuster.” Contestants range from a professional bull rider and a dungeon master to an aura painter and an AI consultant, reflecting the show’s strategy of mixing disparate personalities in a confined, camera-filled environment. As usual, houseguests will compete for a $750,000 grand prize while being filmed around the clock. Following the premiere, episodes will air Wednesdays, Thursdays and Sundays, with live eviction shows on Thursdays. Subscribers to Paramount+ Premium and viewers on Pluto TV can watch continuous live feeds starting July 13. CBS will also introduce “Big Brother: Unlocked,” a bi-weekly companion program beginning July 25 that features former players dissecting the game.