"Starting on April 11, US citizens will be able to select an X as their gender marker on their US passport application, and the option will become available for other forms of documentation next year," Blinken said in a statement. "After thoughtful consideration of the research conducted and feedback from community members, we concluded that the definition of the X gender marker on State Department public forms will be 'Unspecified or another gender identity.' This definition is respectful of individuals' privacy while advancing inclusion."
https://www.cnn.com/2022/03/31/politics/gender-x-passport-applications/index.html
https://www.cnn.com/2022/03/31/politics/gender-x-passport-applications/index.html