Warhammer 40,000: Space Marine 2 is off to a roaring start, but some players are unhappy about one particular point: The game's use of Epic Online Services, which enables cross-play and friends list synchronization between Epic and Steam. Space Marine 2 publisher Focus Entertainment clarified last week that players don't have to link their accounts to play the game, but more recently Epic told Eurogamer that crossplay support is a requirement for any multiplayer games being sold on its store.

“Cross-play across all PC storefronts is a requirement of the Epic Games Store for all multiplayer games, ensuring that players and friends can play together wherever they purchase their games,” an Epic rep said. “Developers are free to choose any solutions that meet this requirement, including Epic Online Services, which may require a secondary installation to enable the Social Overlay (friends lists, cross-platform invites, etc) on PC.” 

In other words, you don't necessarily have to use Epic Online Services for your multiplayer game, but you do have to do what Epic Online Services does if you want to be on Epic's store. 

So while developers are free to come up with their own solutions, an awful lot of them opt for Epic's services because it enables them to avoid reinventing the wheel: EOS meets all the requirements out of the box, and it's free to use. SteamDB lists 944 games currently making use of the client, including Satisfactory, Palworld, Elden Ring, Disco Elysium, Football Manager 2021, Jusant, Armored Core 4, Hogwarts Legacy, and Payday 2.

Epic's rule about PC storefront crossplay isn't actually new: It established the policy in 2023, when it launched self-publishing tools for the Epic Games Store. It also bears noting that Epic Online Services are completely different, and separate, from Epic's decidedly not great launcher. (If that's what you're having issues with, allow me to recommend Heroic, which is really quite good.) 

All that said, if you really want to play Space Marine 2 without Epic Online Services, you can: Responding to one negative review on Steam, a Space Marine 2 developer said EOS “is not a mandatory installation.” It can be uninstalled via the Windows add/remove software menu, although be aware that ditching it will prevent you from playing with people outside of Steam, and may possibly cause other unforeseen headaches in other games.