In a recent update, the United States Department of State has notified that U.S. citizens (USC) who are currently abroad and seeking to return directly to the United States may do so using an expired passport if certain conditions are met.
To take advantage of this temporary relief, the U.S. citizen with the expired passport must fly directly to the United States, a United States territory, or have only short-term transit (“connecting flights”) through a foreign country on his/her direct return to the United States or to a United States Territory. The expired passport should have been originally valid for 10 years or, if the USC was 15 years of age or younger when the passport was issued, then the expired passport should have been valid for 5 years.
The U.S. passport must be undamaged, unaltered and the USC must have physical possession of the passport. This exception does not permit a USC to travel out of the United States with an expired passport. Similarly, this does not permit one to visit any other country using the expired passport. This is only to facilitate the return of a USC stuck outside the United States with an expired U.S. passport.
This update can be found here.