Prior to the change of the child living with you 100%, each parent could claim a Qualifying child dependent for his/her year to claim the child (technically you should have adjusted the custodial time so that the claimant had the child more than 50% of the time).
But, now that you are the custodial parent, in the year your ex wife claims the dependent, she can only claim the Child Tax Credit (only through age 16). After age 16, it will be the $500 "Other dependent" credit.
This may be helpful in your negotiations with the ex:
There is a special rule in the case of divorced & separated (including never married) parents. When the non-custodial parent is claiming the child as a dependent/child tax credit; the custodial parent is still allowed to claim the same child for Earned Income Credit, Head of Household filing status, and day care credit. This "splitting of the child" is not available to parents who lived together at any time during the last 6 months of the year; then only one of you can claim the child for any tax reasons. The tax benefits may not be split in any other manner.
Note in particular that the non-custodial parent can never claim the Earned Income Credit, Head of Household filing status or the day care credit, based on that child, even when the custodial parent has released the dependency to him.
So, it's good idea to let the other parent know that you will be claiming those items, as many first time divorced parents are not aware of this rule and may try to claim those items, which will cause the IRS to send out letters.
Ref: https://www.irs.gov/publications/p17#en_US_2017_publink1000170897
Scroll down to "Children of divorced or separated parents (or parents who live apart)"
You can if you are the custodial parent. The custodial parent is the parent the child lived with for more than 183 nights in 2024 (more than 182 nights in 2023).
