Epic Games confirmed that cross-play across PC storefronts is a requirement for all multiplayer games on the Epic Games Store.

The statement, shared with Eurogamer, reads: "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. 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."

Epic released this statement to clarify Warhammer 40,000: Space Marine 2's usage of an Epic online services. The game installs an Epic Online Services client after the player accepts a EULA, even on Steam. Developer Focus confirmed in a forum post that the Epic client facilitates optional cross-play and syncs friend lists across services. However, linking Steam and Epic accounts is completely optional and will not affect gameplay.