On Wednesday, Steam sent a stealth news update to developers about a surprise new feature coming to Steam as soon as October 21: "Remote Play Together." The feature will transform any "local multiplayer" video game into an online one, and it will work by having the primary player stream their game to up to three other friends—meaning that other players won't have to buy a copy to join in.

As of press time, the emailed update has been posted on a Unity development forum, and it spells out how the feature will work, along with how developers can opt in to its upcoming public beta. The news was later confirmed by Valve developer Alden Kroll as authentic. Valve has yet to otherwise post its own announcement.

How it works

Once the beta goes live, players can pull up the Steam Overlay (shift + tab on a keyboard) while playing a Steam game with any form of "local multiplayer" support and load their friends list. Once you send a Remote Play Together invite, "it's just like handing a second controller to a friend," according to the Valve email.

On a more technical level, the host's computer renders the game in question while also shouldering two other burdens: it must stream its game video to other participants, and it must juggle all incoming buttons and commands from other players. Valve's email promises that the feature will support a 1080p video signal sent to other players at a 60 frames-per-second refresh, though all players must have at least a 10Mbps connection for "a successful low-latency connection."

For a better sense of how this will work, imagine a multiplayer game like Rocket League, which has a local split-screen mode for four players. Using Remote Play Together, the host computer will render that game's default split-screen content, immediately stream that signal to three other machines, and process the other players' button taps as if their gamepads or keyboards were directly connected to the host. All players will see the exact same gameplay screen. This differs from normal online Rocket League, which gives every player their own dedicated screen, because Remote Play Together simulates the "everyone on the same couch" experience.

But how will Remote Play Together feel in action? We've tested upcoming game-streaming services like Microsoft Project xCloud and Google Stadia, which bounce video and button taps between your home device and a presumably optimized server farm. In those demos, which we tested in controlled expo halls, we've noticed everything from near-perfect connections to noticeable, tolerable latency. Can Valve's version possibly keep up, especially when it will ask "host" PCs to juggle game rendering, video streaming, and input translation?

There's a reason that many latency-sensitive games have landed on Steam without online support; if you have to wait for packets to bounce back and forth between a host and a client, then all the fun can get sucked out, especially for twitchy versus games. (Indie couch co-op games, in particular, tend to skip online modes due to the headache they can be for a small studio to code and implement.) But Valve is clearly bullish on the idea that its feature will be fast enough; one of the biggest local-multiplayer games of the past decade to never receive an online mode, Towerfall, is clearly shown in one of the company's sample images.

Valve's explanatory email says the beta will launch "the week of October 21" for all users of the Steam Client Beta (which can be opted into in Steam's settings menus). So long as a shipped Steam game includes a tag for "local co-op," "local multiplayer," or "split-screen," it will automatically be supported. After confirming that only one participating player needs to own a particular game, Valve's email offers an assurance in terms of game sales: "We don’t believe it’s feasible to use Remote Play Together to avoid purchasing games on Steam entirely, and like other promotional tools and features, we believe the additional exposure and fun players have will lead to additional revenue and player growth." If that's not comfort enough, developers must contact Valve to opt out of their games automatically appearing in this beta.

Should the email's release date come to fruition, we won't need to wait long to see how well this mode works, whether its image quality suffers, and whether it's superior to existing options like Parsec.