Airbus is preparing to detail a series of changes to the A321neo which will take its range beyond the 4,000nm (7,400km) offered by the A321LR version.
The airframer appears increasingly likely to unveil the aircraft during a first-day event at the Paris air show on 17 June.
FlightGlobal understands that the airframer would focus initially on a single variant, the A321XLR, with larger-volume additional centre tanks evolving from simplified internal structures.
While Airbus declines to comment, a source familiar with the development says that "most of the changes are inside", although aerodynamic modifications to the wing or wing-tips "would make sense".
Commercial discussions still being finalised on the eve of the show.
Airbus already has nine weight variants of the A321neo. Seven of these, with maximum take-off weights ranging from 80t to 93.5t, are listed for the basic aircraft.
Two other variants are listed for the 'Cabin Flex' configuration of the A321neo, including the current long-range A321LR option with a 97t MTOW – the highest weight so far for the type.
Airbus has indicated that an even longer-range option would take the MTOW above 100t and potentially push the aircraft's capability to 4,700nm.
Its basic A321neo has fuel capacity of 23,490 litres but the A321LR uses three additional 3,121-litre centre fuel tanks to take total fuel to 32,853 litres.
The airframer has been focusing on strategies to increase the fuel carriage of the aircraft and ways to extract range through aerodynamic enhancements.
CFM International and Pratt & Whitney power the current A321neo variants including the A321LR.
Pratt & Whitney president Bob Leduc tells FlightGlobal that its geared-turbofan PW1100G engine is "the right choice" to power a longer-range version.
"It provides the highest level of fuel efficiency, so for longer missions the fuel savings will only increase," he adds.
CFM builds the Leap-1A and executive vice-president Allen Paxson simply says the company is "continuing to develop" technologies, materials and aerodynamics to be "ready for whatever comes next".
Airbus has yet to disclose launch customers for the aircraft, but has previously indicated that initial deliveries would take place around 2023-24.