If the annual CES technology show in Las Vegas were a high school dance, Amazon.com Inc. and Alphabet Inc.’s Google would be the kids who stayed away, preferring to throw their own parties. Only this year, the tech giants are all dressed up and looking for dates.

They’re seeking and supporting partners for their voice-operated platforms, Amazon Alexa and Google Assistant. In the grand tradition of such classic battles as Android versus iOS and Mac versus PC, there’s a showdown in the voice-operated world over who’s going to be in charge of your home.

Despite CES’s role as an international meeting place for digital giants and startups alike, the titans of tech—not just Google and Amazon, but Apple Inc., Facebook Inc. and Microsoft Corp.—have been largely absent in recent years. They might have sent staff, but they didn’t set up big tents or booths, or buy big ads to cover Vegas buildings. Microsoft once dominated the tech show, but pulled back its public-facing activities after 2012.

“Both Google and Amazon kind of thought it was cool not to go to CES,” said Patrick Moorhead, chief analyst with Moor Insights & Strategy. “But it’s a required thing because of this new plane of competition in home automation and digital assistants.”

CES will be the ideal battleground this week, with 3,900 exhibitors, many showcasing home products with voice-operated capabilities—not just speakers but entire entertainment systems, kitchen appliances and security platforms. But since making and supporting a reliable voice assistant can cost billions of dollars, even well-heeled companies with broad product lines are pairing with the industry leaders.