If you didn't pay the ES for Q2-4 then AI method won't eliminate the penalty. If it was just a Q4 event I would have thought it would reduce the penalty as it would show the income coming later in the year rather than assumed to be evenly happening during the year; but the AI method will conversely penalize you on Q1 as it moves all that income earlier rather than assuming it was even thru the year; so maybe some of it ends up a wash depending the amounts. I fell into AI method last year due to a Roth conversion and it worked out as it lined up with a high Q4 ES, but was a lot of work I hope to avoid again. If you expect volatile income to the upside then paying ES based on prior year (100% or 110% if AGI > 150k) is more predictable and since ES are known and fixed, the timing of additional income events the following year doesn't matter.
The penalty rate is 8% but I think as you found this gets averaged out if you look in total due to the quarterly underpayment calculation, but if you miss Q1 ES you would see a higher penalty impact than missing Q4 ES.
(probably things you already know but thought I'd chip in)
