The NAFTA C of O will no longer be used for USMCA shipments. The USMCA does not require a specific certificate of origin form. Rather, it requires nine specific data elements, which can be presented in any format, similar to other more modern trade agreements that were implemented subsequent to NAFTA [See USMCA Ch. 5 ‘Origin Procedures,’ Art. 5.2 (Claims for Preferential Tariff Treatment) and Annex 5-A (Minimum Data Elements)]. To avoid confusion, the CBP Form 434 (NAFTA C of O) will no longer be accepted for claims of preferential treatment under the USMCA. Even if the rule of origin for the subject good is the same under NAFTA and USMCA and all of USMCA’s required data elements are present on Form 434, the good needs to be recertified under USMCA.
Visit the CBP website for more information, there is an FAQ at the bottom which is very helpful answering questions. You will also find a comment & question request box to the bottom left that can be used to ask a question directly to CBP.