Kate Bolduan’s next shift on CNN hasn’t started quite yet, but she’s acting as if it has. A group of cameras is flocking around the news anchor in a New York studio that has recently been updated, and she presses producers to let her rehearse a story she needs to have mastered by the time she gets on air. “We don’t want to get this half right,” she tells those listening to her.

Neither does the news network.

Bolduan and five of her on-air colleagues, along with dozens of crew members and producers working in New York, Washington, D.C. and Atlanta, are taking part in a major TV-news experiment that is going to play out each weekday for the foreseeable future at CNN. The question the Warner Bros. Discovery network is trying to solve: How to keep viewers watching TV news when they have video...