How will my Bonus be recorded on my W2?

Bonus on W2

The vested amount is considered as income by the IRS. Any bonus amount that is vested within a given year will be reflected on that year’s W2. 

If your vesting happens on December 5th for example, your next paystub will contain an entry for the amount that has vested and your employer will cover the tax portion of this income as described in this article, as applicable.