If you live together, either one of you may claim the child, but not both. A stepparent has the same legal rights to claim a child as a dependent as a biological child, and this right continues even if you divorce the other parent.
if you can’t agree and both claim the child, the IRS will apply the tiebreaker rules and award the dependent to the parent with the higher income. But if you both agree that you should claim the child, that’s fine, even though your income is lower.
If you are living apart, then generally speaking, only the parent where the child lives more than half the year can claim a child as a dependent.
