No, you do not "check-in" with an itinerary in 2026; you check-in with your Boarding Pass or a Confirmation Code (PNR). While a flight itinerary is a useful document that summarizes your travel dates, flight numbers, and times, it is not a legal travel document. To check-in, you typically enter your 6-digit confirmation code into the airline's app or a self-service kiosk at the airport. This process then generates your Boarding Pass, which is the only document (alongside your ID or passport) that allows you to pass through security and enter the aircraft. However, an itinerary is still vital for International Travel and Visas; border agents or embassies often require a printed copy of your full flight itinerary to prove you have a return flight booked and do not intend to overstay. So, while you don't "use" it to board the plane, you should always have a digital or physical copy of your itinerary ready for customs officials or for your own reference during the trip.