YouTube has a deal to buy Twitch, a popular videogame-streaming company, for more than $1 billion, Guru3d.com reported, citing sources familiar with the pact.

The deal, in an all-cash offer, is expected to be announced imminently, sources said. If completed the acquisition would be the most significant in the history of YouTube, which Google acquired in 2006 for $1.65 billion.

San Francisco-based Twitch lets users upload and watch free, live gameplay videos that can be streamed from Microsoft Xbox and PlayStation 4 consoles. The company claims to have more than 45 million monthly users, with more than 1 million members who upload videos each month.

YouTube is preparing for U.S. regulators to challenge the Twitch deal, according to sources. YouTube is far and away the No. 1 platform for Internet video, serving more than 6 billion hours of video per month to 1 billion users worldwide, and the company expects the Justice Department to take a hard look at whether buying Twitch raises anticompetitive issues in the online-video market.

Twitch was launched in June 2011 by Justin Kan and Emmett Shear, co-founders of Justin.tv, one of the first websites to host livestreaming user-generated video. Shear currently serves as CEO of Twitch.

Founded in 2011, the startup has raised about $35 million in funding. Investors include Bessemer Venture Partners, Alsop Louie Partners, WestSummit Capital, Take-Two Interactive Software, Thrive Capital and Draper Associates.