You are not required to give them anything unless they sued you and/or get a court order or issue discovery to you. If you are trying to settle the debt they will probably want some proof of your inability to pay the whole thing for them to agree. But - you aren't technically required to do anything unless they sue you.
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They can request the information if they obtain a judgment and then file an information subpoena to locate assets. By the way 401 k and IRAs are exempt assets if you file a bankruptcy and you can kept them.
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