Do I say dependent lived with me for the whole year if I'm not the custodial parent but have agreement to claim dependent with ex spouse?

[ThomasM125]

No. You can claim the dependent though if you have an agreement with the ex-spouse. You will see a screen when you enter the dependent's personal information where you can say that you have a custody agreement and that will allow you to claim the dependent if all the other requirements are met:

[Opus 17]

Claiming that the child lived with you would allow you to claim certain tax benefits of the dependent that you are NOT entitled to, because they only stay with the parent who has physical custody more than half the year.  Doing that will also likely cause an e-file conflict, that blocks you or the other parent from filing, and will result in an IRS investigation.  Answer No (if that's the case) and then answer the follow up questions.  You will have to mail your signed form 8332 or signed agreement to the IRS after e-filing, use a mail service with tracking.