American Airlines is now the second U.S. carrier to offer non-binary gender options to passengers during the booking process.
The airline recently completed a system update to allow the change, which now carries four options for gender: M, F, U or X, an American Airlines spokesperson told ABC News in a statement.
"Taking care of our customers and team members is what we do, and we are glad to be able to better accommodate the gender preferences of our travelers and team members," the spokesperson said.
United Airlines began offering non-binary gender booking options in March, one month after industry trade group Airlines for America (A4A), and members of the International Air Transport Association approved a new standard to account for non-binary identification.
Gender during booking should match the ID that will be used at the TSA checkpoint, according to American Airlines. Passengers can update their gender through the airline's reservation team, and the options will be rolled out online in early 2020.
Southwest Airlines and Delta Airlines also plan to instate similar options.
The TSA began requiring passengers to enter their gender and date of birth when booking flights in 2009, which was a result of 9/11, when the administration created the Secure Flight vetting program.
ABC News' Elizabeth Thomas contributed to this report.