Boeing will at the Paris air show unveil the 350-seat 777-8X as an ultra-long-range airliner with slightly more stamina than the 9,400nm (17,400km) capability of the 300-seat 777-200LR.
The 777X family - including the 8,000nm-range, 400-seat 777-9X - will also feature an all-new interior architecture, with a special focus on helping airlines generate cash from onboard services.
Boeing is rolling out more details of the proposed 777X family ahead of a formal launch expected later this year and perhaps timed with the Dubai air show.
The final 777-8X configuration appears to borrow heavily on the 777-8LX concept, as a direct replacement for the 777-200LR but with the seating capacity of the 777-300ER.
Mike Bair, Boeing senior vice-president of marketing, says the proposed 9,500nm range for the 777-8X is coveted by airlines that "live in sandy, hot places". The additional range comes essentially for free, he says. It is the natural consequence of sharing the maximum take-off weight, engine thrust and wing of the 777-9X, but with a shorter fuselage.
"We didn't point-design this airplane to do 9,500nm, it kind of fell out that that's what it was going to do," Bair says.
Airlines that chose the 777-8X could also trade-off range for more belly cargo capacity, Bair says. Like the 777-200LR, the 777-8X will be the variant Boeing eventually modifies into a main deck freighter, he says.
The 777X will be powered by the 100,000lb-thrust (445kN) class General Electric GE9X turbofan and feature an all-composite wing derived from the 787, with each of those upgrades generating half of the fuel-burn efficiency improvement that Boeing claims over the 777-300ER, Bair says.
Other changes to the architecture of the aircraft will be minimal. Although the 787 introduced a more electric architecture, the 777X's systems will be modelled closely on the 777-300ER. Boeing is considering an aluminium-lithium structure for the fuselage, but has no plans to alter the cross section or switch to an all-composite airframe, Bair says.
The interior of the 777X, however, opens up more possibilities for innovation. Boeing realises the 787 interior will be 15 years old when the 777-9X is introduced in 2020.
"We're not going to repeat the  interior on the 777-9X, or -8X. We're going to take the next step," Bair says. "There's some really exciting things that may be able to happen in terms of utilising where electronics are going to help the passenger experience."