Per an announcement via the Anno Union community portal, the upcoming Anno 1800 will only be available on Uplay and the Epic Games Store post-launch. Steam preorders will still be available through April 16th, up until release. Furthermore, Steam players will get all content and balance updates concurrently with other platforms and will be able to play with friends on other storefronts. Curiously, the Anno 1800 open beta, slated to run from April 12 through the 14th, will only be available on Uplay and the Epic Games Store.
The full comment as made on the Anno Union site is as follows:
Following the successful launch of Tom Clancy’s The Division 2 on PC on the Ubisoft Store and the Epic Games store, we are announcing today that we are partnering with Epic Games on Anno 1800 as well. Players can now pre-order the Deluxe and Standard editions of Anno 1800 on PC on the Epic Games store. Moreover, all players will be able to try Anno 1800 via the Open Beta, scheduled from April 12 to April 14, by downloading the game on Uplay or via the Epic Games store. Once the game has been released on April 16, 2019, Anno 1800 will only be available digitally on the Ubisoft Store and the Epic Games store. Pre-orders on Steam can be made until the release of the game. Everyone who pre-ordered Anno 1800 on Steam will be able to play the game upon release and will automatically get all future updates and content.
It is worth noting that Ubisoft says there are no plans to remove any older Anno titles from Steam. Epic previously promised that they wouldn't want to pull a game so soon before launch again, as was the case with Metro Exodus. Clearly, as now both Exodus and Anno 1800 were moved just a mere 18 days before launch, it's hard to imagine this playing out well for either Ubisoft or Epic.
For what it's worth, Epic did announce at GDC that they would be partnering with Ubisoft to bring future and catalogue items over to the Epic Games Store. Many assumed this meant that Steam gamers wouldn't get shut out of Ubisoft games, as was already the case with The Division 2. Still, Ubisoft's moves have been paying off for them, as preorder numbers for The Division 2 were higher overall than its predecessor, especially on Uplay.
Furthermore, regardless of your feelings on Epic's exclusivity arrangements, Epic themselves reported higher sales for games like Metro Exodus. Whether this is imagined as a sort of PR goodwill, or perhaps effective marketing is hard to say. Still, these deals can cause division and strife in the gaming community at large, especially when games are moved without prior warning. We've reached out to employees at Valve, Ubisoft, and Epic Games, and will update this story, should they respond.