Airbus has shrugged-off criticism over its redesign of the A350-1000, insisting it will not keep changing the twinjet simply to appease individual customers.
Emirates and Qatar Airways, each of which already had 20 A350-1000s on order before the revamp, have been particularly harsh about changes to the aircraft.
Influential leasing chief Steven Udvar-Hazy has also questioned the type's ability to compete with the Boeing 777-300ER.
However, Airbus chief Tom Enders, speaking to Flightglobal at the airframer's Broughton wing plant in the UK, said the manufacturer had "fought long and hard" to achieve the current configuration.
"For us, that is the solution," he said. "We're not going to redesign it every half-year."
Airbus's redesign efforts have concentrated on the Rolls-Royce Trent XWB engines, which will have a higher thrust capability but will lose commonality with the powerplants for the -900 and -800 variants.
Adjustments to the wing and an increase in maximum take-off weight, will also feature in the revamp. The airframer aims to give the aircraft an additional 400nm range (740km). Etihad Airways has 25 A350-1000s on order, while Korea's Asiana has the remaining 10.
Enders also gave the clearest indication yet that the A350 could miss its end-of-year target date for starting final assembly, after insisting the aircraft would not be rushed into unmanageable production.
He stressed that the A350 involved a "big jump" in technology and "a lot of unknowns".
"There's no magical date by the end of the year," he said. "It's nice to keep to a schedule but it's more important that we have a manageable level of outstanding work. We shouldn't reach the stage where [assembly] isn't manageable."
Executive vice-president for programmes Tom Williams said the airframer was still expecting "sections on the final assembly line by the end of this year".
However, he said the aircraft involved "a lot of innovation" and added: "Clearly that's been difficult."
He admitted that achieving a "flyable aircraft" by the end of 2012 was "tight", and added: "We're down to short straws."
Broughton has taken delivery of wing components for the first flying example, MSN1, but initial final assembly will focus on fuselage sections for the A350 static test aircraft.