Marvel's Avengers paid XP boosts were supposed to stay out of the game, Square Enix promised. However, that's apparently changed (thanks, VGC). Following Avengers' launch on Xbox Game Pass, you can now buy consumable items, including XP boosts, with real-world money if you're so inclined.
We don't really recommend it, though.
While it seems like a common enough practice for service games - just look at the likes of Genshin Impact - the problem is Square Enix outright promised not to do this in 2019.
Marvel's Avengers Paid XP Boosts Are a Thing Now
A blog post in August confirmed the game's stance on only offering cosmetics for purchase:
We’ve committed that content purchasable with real money in Marvel’s Avengers will be aesthetic-only additions, which will ensure we can keep the game fresh for years to come," . For some, the writing had been on the wall for a while, as Crystal Dynamics slowed down the rate at which players were able to increase their level in March 2021.
Shortly before that, Crystal Dynamics' studio lead Scot Amos told GamesIndustry.biz the point of avoiding paid XP and other consumables was to encourage experimentation.
"Your Black Widow could be different to my Black Widow – just a little, maybe a lot depending on what you favour and how you unlock things," he said. "In terms of how we monetise, we’ll have cosmetics. No gameplay paywalls.”