https://wccftech.com/doom-eternal-primarily-online-free-events-seasons/

Last week it was announced that Doom Eternal, like most modern AAA games, will let you earn a wide variety of (sometimes rather wacky) cosmetics. But how will you actually get said cosmetic goodies? Well, in a new dev diary id Software’s Marty Stratton and Hugo Martin describe how the game’s live-service elements will work. Check it out for yourself if you have a few minutes to spare.

Basically, players will be able to earn XP by playing all the game’s modes, including the story campaign and Battlemode multiplayer. It’s implied Doom Eternal will be getting a variety of free add-on content, limited time events, and at one point, Stratton mentions seasons, so yeah, it will be your standard “games as a service” approach. Here’s a bit more detail: