Shares of Roku jumped more than 3% after hours on the news.
For users with the current HBO app, the channel will automatically update to HBO Max. Otherwise, Roku users will be able to download the HBO Max channel on their Rokus. Existing users can log in using their current credentials, while new users can sign up through the app for $14.99 a month.
Last week, AT&T CEO John Stankey said HBO Max now has 12.6 million users, far behind the 86.8 million Disney+ subscribers. Roku has more than 46 million active accounts and could help HBO Max boost its users.
HBO Max is also set to get a lot more content. Earlier this month, AT&T's Warner Bros. announced that all of its films scheduled to launch in 2021 will be released on HBO Max at the same time they hit theaters. That also applies to "Wonder Woman 1984," which lands in theaters and on HBO Max on Dec. 25.