When Google executive Mario Queiroz unveiled a new voice-controlled virtual assistant, Google Home, at the company’s developer conference this month, he left out a key detail: Home is a dressed-up version of Chromecast, the video-streaming device Mr. Queiroz’s team previously developed.

The guts of Home, including its ARM-based microprocessor and Wi-Fi chip, will be the same as those in the Chromecast, says a person with direct knowledge of the plan. In other words, Home will essentially be a microphone, speaker, plastic top with LED lights and a fabric or metal bottom—wrapped around a Chromecast.