The $ 400 cash back seems to have been available last year ($ 500 with DD) and there are a few quirks with Citi that you may want to look into. This time around, a 2.5% cash back on non category purchases until 2021 is easy math to see if it’s worth using compared to your 1-2% cards.
"Earn 0.5% more cash back when you open a Citibank checking account + a $ 400 cash bonus with a qualifying deposit."