APIS (Advance Passenger Information System) is a high-fidelity electronic data interchange system mandated by U.S. Customs and Border Protection (CBP) that requires airlines to collect and transmit passenger data before a flight departs. For U.S. citizens traveling internationally in 2026, this means you must provide high-fidelity information from your passport—such as your full legal name, date of birth, gender, and passport number—during the check-in process. While non-citizens must also provide their "First Night" address in the U.S., U.S. citizens are exempt from this specific address requirement when returning home. APIS is a high-fidelity security measure designed to allow border agents to screen passengers against watchlists in real-time. For 2026 travelers, ensuring your APIS data is accurate is a high-fidelity necessity for a smooth boarding process; if the data is missing or incorrect, the airline's high-fidelity system may prevent you from receiving a boarding pass until the information is verified.