IRS Link to Form — Found Here

Form 706 is the Estate Tax return, and it has a section concerning Generation-Skipping Transfers.

706 GS (D), specifically, is the form which 706: GS (D-1) is the corresponding form if the transfer is associated with a trust, which is filed by the trustee.

The Generation-Skipping Tax attempts to prevent an estate from transferring too many assets directly to grandchildren instead of children for the purpose of shielding heirs from estate taxes. The form for reporting Generation Skipping Transfers is 706 GS (D), where 706 is the Estate Tax Return filing.

706 GS (D-1) would be filed by a trustee in the event that a trust rather than the estate was responsible for making the transfer. There is a slightly higher tax (about 10% higher) on generation-skipping transfers as opposed to regular transfers.