The 407–passenger 777-9X should stretch the 777-300ER by four frames to 250 ft 11 in (76.48 m) in length, for a 759,000 lb (344 t) maximum take-off weight (MTOW) and powered by 99,500 lbf (443 kN) engines, targeting per-seat 21% better fuel burn and 16% better operating cost.

In 2011, Boeing refined its response to the revamped Airbus A350 XWB with three 777X models, targeting a firm configuration in 2015, flying in late 2017 or 2018, and entering service by 2019. The 777-9 first flew on January 25, 2020, with deliveries delayed multiple times and expected to begin in 2025.

As of February 2023, there are 363 total orders for the 777X passenger and freighter versions from ten identified customers and other buyers. The 777X program was proposed in the early 2010s with assembly at the Boeing Everett Factory and the wings built at a new building adjacent to the Everett factory. The 777-8 provides seating for 384 passengers and has a range of 8,745 nautical miles (16,196 km 10,064 mi) while the 777-9 has seating for 426 passengers and a range of over 7,285 nmi (13,492 km 8,383 mi). The 777X was launched in November 2013 with two variants: the 777-8 and the 777-9. The 777X features new GE9X engines, new composite wings with folding wingtips, greater cabin width and seating capacity, and technologies from the Boeing 787. The Boeing 777X is the latest series of the long-range, wide-body, twin-engine jetliners in the Boeing 777 family from Boeing Commercial Airplanes.

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