It's a bit more complicated with arbitration.
First, you've got the one season aspect, or two seasons if the team wants that. They probably would, but who knows.
Next, one of his main comps, Oettinger, only makes $2.4m in the first year of his contract (this season past). Oettinger played 48 games the season prior to making that $2.4m.
So, the arbitrator would look at that, Knight's deal with a team incapable of being fiscally responsible with goaltenders and every other mid-20s contract signed prior. It's not often the arbitration ruling comes back at the highest dollar value contract signed among the player's peers.
So, while Swayman may come in above $4m, I'd say it's safer and likely more accurate to say it'll come in around $4m. And Oettinger's $2.4m, backloaded deal may be huge.