As a response to a question from a fan, the Twitter account of the upcoming game stated there will be full Redfall crossplay between Windows PC and Xbox Series X|S players regardless of how they purchase the title.
When the game makes its debut, players on Xbox Series X|S will be able to play against PC players via PC Game Pass, Steam and Epic Games Store.
This response proves a clearer explanation than the one seen on the Community Q&A Wrap-Up post on Bethesda.net. The response on the website says, “you can definitely play with your friends on Steam.” The original version of the response is shared on the tweet.
[Source]: @playRedfall (Twitter): Crossplay confirmed between Xbox + PC Game Pass + Steam + Epic Game Store – [Archive] – [Screenshot]. Bethesda.net: #AskArkane – Community Q&A Wrap-Up – [Archive] – [Screenshot].