In a statement made at the International Conference on Nuclear Security in Vienna, U.S. Secretary of Energy Ernest Moniz announced that "the United States is beginning consultations with the IAEA to monitor the dilution and packaging of up to six metric tons of surplus plutonium at the Savannah River Site (SRS) in Aiken, South Carolina."
The material in question is part of the U.S. plutonium stock that was designated excess for military purposes. In addition to the 6 MT of non-pit plutonium covered by the current initiative, it also includes 34 MT of pit plutonium that was to be disposed as part of the U.S.-Russian Plutonium Management and Disposition Agreement (PMDA) as well as 7.1 MT of pit plutonium for which a disposition path is not yet assigned. The Department of Energy announced its intent to dispose of the 6 MT of non-pit plutonium in January 2016 (a formal record of decision was published in April 2016).
It appears that the United States will invite the IAEA to monitor the activities at the Savannah River Site, which include "blending the plutonium oxide with an adulterant, packaging the diluted materials in secure canisters, and preparing the canisters for permanent disposal in a geologic repository." The initiative does not seem to cover subsequent placing of the canisters in the WIPP geologic repository. [UPDATE 12/10/2016: U.S. officials indicated that the Unites States will be open to IAEA monitoring of the emplacement of plutonium to WIPP.]
The statement also does not say if the IAEA monitoring will be applied to the 34 MT of plutonium that was covered by PMDA. In 2010, the United States and Russia informed the IAEA of their intent to develop verification measures with respect to their disposition programs, but this arrangement is now in question after the United States indicated its intent to change the disposition method and Russia suspended the agreement in October 2016. It is likely that if PMDA is terminated, the United States will extend the transparency measures of the current initiative to the 34 MT of the plutonium as well. The statement make an implicit commitment to do so, as it states that "the total amount of surplus plutonium for which the United States has committed to verifiably eliminate to 40 metric tons."
Note that the Savannah River Site has already packaged some plutonium and prepared it for shipment to WIPP. Since this process began before the 2016 decision regarding surplus plutonium, it is not included in the 6 MT covered by the new initiative. As of the end of 2014, WIPP accepted 5.7 MT of plutonium.