The United States of America undertakes with regional partners to develop a definitive, mutually agreed plan with at least USD 300 billion for the ​reconstruction and economic development of the Islamic Republic of Iran. The mechanism for the implementation of this plan will be finalized as part of final deal within 60 days. All required licenses, waivers, and permissions needed for the relevant financial transactions will be granted by the United ​States of America.

Note that this suggests that VP Vance's recent claims of effectively "the gulf states will pay for it" is NOT in the language here. From my reading, if that amount cannot be brokered with those countries, the US still ends up holding the bill, since there is a 60-day deadline and failing to broker it would violate the terms of the peace agreement.

I'm not seeing how there isn't a significant chance that the US taxpayer directly funds this line item. In fact, the point of having Vance make such comments is probably to assuage at least their own base, so they aren't paying attention in 60 days when the money has to come from somewhere.