United First is available only on flights within the U.S. and Canada. United Business class is available on flights between the U.S. and Latin America or the Caribbean, as well as some U.S. transcontinental flights. The first and business class offerings are quite similar.

United Airlines' cabin structure depends entirely on whether you are flying domestically or internationally. On domestic flights, United offers a cabin officially called United First®, which features wider leather seats, priority service, and complimentary meals on longer routes. However, on long-haul international flights, United does not offer a traditional "First Class." Instead, their flagship premium cabin is United Polaris® Business Class, which features 1-2-1 direct aisle access and lie-flat pods. While some other global airlines still maintain a four-class system (Economy, Premium Economy, Business, First), United—like most US carriers—has consolidated its most luxurious international offering into the Business Class experience. For certain short-haul international flights (like to Canada, Mexico, or the Caribbean), the premium cabin is marketed as United Business®, which is essentially the same as the domestic First Class seat. So, if you are looking for a "suite in the sky" on a flight to London or Tokyo, you are booking Polaris Business, not First Class.