Airbus's new Beluga XL transport will be some 4.3m longer than the A330-200 on which the aircraft will be based.
The Beluga XL, which will succeed the smaller A300-600ST within the airframer's logistics fleet, has reached design freeze.
Airbus has disclosed that it will be 63.1m (207ft) in length while its wing span will remain unchanged from the A330-200's at 60.3m.
The aircraft's next development stage will be the detailed design freeze.
Airbus says a review has shown that the Rolls-Royce Trent 700-powered jet is sufficiently "robust and mature" to move out of the concept phase.
Final assembly is scheduled to begin in 2017.
The Beluga XL will be around 1.5m taller at the fin than its A330 counterpart.
Airbus projects that it will have a maximum take-off weight of 227t compared with 155t for the current A300-600ST.
The XL, with an 8.8m-diameter fuselage, will be able to transport a maximum payload of 53t over a range of 2,200nm.
Programme chief Bertrand George says the aircraft's development has benefited from a "new and innovative" way of working with suppliers.
"By working together as a fully integrated team in a single location, we have maximised our efficiency," he says.
Airbus expects to put the Beluga XL, of which it will construct five, into service in 2019.