Airlines have criticized the planemaker's one-size-fits-all policy that would see the mid-sized A350 built in three separate models all using the same engine, the Rolls-Royce Trent XWB.
Until now, Airbus and Rolls have defended the engine as an all-rounder capable of powering twinjet A350 planes carrying 270 to 350 people, competing with two different types of planes manufactured by rival Boeing
But the range needed from one type of engine became daunting as airlines called for more thrust for the largest A350-1000, allowing it to fly further with more weight.
My understanding is that Rolls-Royce has agreed to build a new engine, the chief executive of a major A350 customer told Reuters at an airline industry event.
A spokesman for Airbus declined comment. A spokesman for Rolls-Royce in Singapore was not available for comment.
A new engine typically costs up to $2 billion to develop, according to engine industry executives.
An industry source familiar with the project told Reuters in November that Rolls was looking at two variants of the same engine, which would be less costly than building from scratch.
But it remained unclear how many components would be shared between old and new models or who would pay for the upgrade.
The head of a second customer airline said he was awaiting details of the changes to the A350, but noted Airbus needed to juggle several variables to get the technical ingredients right.
One of the world's most influential aircraft buyers, leasing magnate Steven Udvar-Hazy, said he expected Airbus to modify its plans for the A350 and that this could lead to delays.
They have to address payload, range and runway performance, the chief executive of Air Lease Corp
Airbus last month canceled a media briefing on the A350 and said it would issue an update at the Paris Air Show in June. The aircraft has undergone numerous design changes in its history.
The Trent XWB is the latest and physically largest member of the Rolls engine family which powers the world's biggest jets.
With a fan wider than Concorde's fuselage and built to devour more than a tonne of air every second, the engine claims to be among the most powerful and flexible in civil aviation.
But engines are designed to work most efficiently in a certain band of thrust and critics have said the Trent XWB would find it difficult to operate efficiently across all three types of A350, even before the A350-1000 is beefed up.
First indications of a change in strategy were disclosed by industry sources in November. The final decision could set the tone for the engine market in the next decade, with implications for the rivalry between Airbus and Boeing.
Airlines say a beefed-up A350-1000 would be better able to compete with the Boeing 777 mini-jumbo, one of Boeing's most successful models, while the smaller A350-800 and A350-900 aim to tackle the 787 Dreamliner, due to enter service this year.
Rolls' rival General Electric