From the FAA:
“The FAA will implement flight plan filing for civil aircraft using a format that aligns with International Civil Aviation Organization (ICAO) standards. The new format appears on FAA Form 7233-4, FAA International Flight Plan (Revision 7/2015). Aligning our flight plan similar to the ICAO format will allow integration of new capabilities such as Performance Based Navigation (PBN).”
Here’s a link to the new form; and here’s a link to simplified instructions on how to fill it out.