Even if you want to play Redfall alone, you'll need a constant internet connection.
Bethesda confirmed as much in a newly updated Redfall FAQ. "A persistent online connection is required for single player and co-op," it reads, cementing Redfall as an always-online game. You'll also need a Bethesda.net account to link to your Steam or Xbox profile, so if you don't have one already, you'd best get one set up if you plan on hunting vampires in Arkane's latest sandbox.
Though it's not the discourse firestorm it once was, "always-online" is still something of a dirty word in games, and not entirely without reason. Rather than concerns around internet access – still an issue for a non-trivial portion of gamers, to be fair – I'd wager more people are worried about being able to access always-online games themselves.
When a constant connection is mandatory, a server outage can block you from playing a game you were enjoying by yourself. This certainly wouldn't be the first time, but that kind of restriction still feels weird when solo play is your focus, and I'd imagine it caught some people off-guard after Bethesda's assurances that Redfall will satisfy fans of single-player Arkane games like Dishonored.
There's also the issue of longevity and preservation. Nevermind a temporary outage; if your ability to play a game solo is explicitly tied to its servers, you'll be out of luck if those servers are taken offline after a game is sunset. That's not an immediate concern for Redfall, and many modern games – like the recently sunset Marvel's Avengers – keep the servers on even after actual updates stop, but structurally speaking, it's never a bad thing to have an offline option. That said, with how online-focused modern gaming has become between live service releases, cloud and subscription services, and general multiplayer, this news likely won't bother many Redfall fans.
Arkane just revealed the Redfall Bite Back edition which comes with additional cosmetics and weapons, not to mention future characters.