Hastening Arms Limitations Talks Act of 2021 or the HALT Act of 2021 This bill prohibits the obligation or expenditure of funds to conduct an explosive nuclear weapons test that produces yield unless (1) the President details any change to the condition of the U.S. nuclear weapons stockpile from the previous year, and (2) Congress enacts a joint resolution approving the test. Further, the bill declares it to be U.S. policy to lead international negotiations on specific arms-reduction measures.