The 2017 Paris Air Show was expected to be focused on narrowbody aircraft, and Day One did not disappoint. The MAX vs. neo battle took center stage.

Boeing launched the 737 MAX 10, the fourth and largest variant of the re-engined family of aircraft powered by CFM International LEAP-1B engines. It is 66 inches longer than the 737 MAX 9, will be able to seat up to 230 passengers and have a range of 3,215nm with one auxiliary fuel tank. Boeing said it has already secured more than 240 commitments for the MAX 10, including MOUs from Indonesia’s Lion Air for 50 and India’s SpiceJet for 40.

“Our customers told us to build it bigger … and that’s exactly what we’re bringing to the market,” Boeing Commercial Airplanes president and CEO Kevin McAllister said. Boeing is claiming a 5% seat-mile cost advantage over the Airbus A321neo.

But Airbus COO-customers John Leahy immediately shot back that “the MAX 10 is a competitor to the MAX 9, not to the A321neoLR.” He added, “Comparing the A321neoLR vs. the MAX 10: we have 10 more seats, more range—plus 1,000nm—and up to 10% lower fuel burn.”

The momentum of the A320neo program continued at full pace as Airbus kicked off Le Bourget with an order from GE Capital Aviation Services (GECAS) for 100 A320neo family aircraft, bringing GECAS’ total commitment for A320neo family aircraft to 220 aircraft, a mix of A320neos and A321neos.

Airbus COO and president-commercial aircraft Fabrice Bregier called GECAS’ latest order “a very strong mark of confidence” for the neo program. GECAS president and CEO Alec Burger said feedback from airline customers on the A320neo has “so far been extremely positive in terms of fuel efficiency and noise abatement.”

Meanwhile, Boeing said it was “very satisfied” with the early in-service performance of the 737 MAX 8 with Malaysia’s Malindo Air, which launched the MAX program into commercial service last month. Boeing VP and GM-737 MAX program Keith Leverkuhn said fuel consumption performance so far was as expected “or slightly better.”

The strength of the MAX and neo programs, and the narrowbody market generally, is enabling Boeing and Airbus to have solid and active starts to the Paris Air Show despite weakness in the widebody sector, where orders have stalled and some deliveries have been pushed back amid fears of overcapacity.

Interestingly, the MAX and neo (particularly the A321neoLR, which will be able to fly around 206 passengers in a two-class layout on routes of up to 4,000nm) are essentially giving airlines a “widebody light” option in which long-haul routes previously only viable with a widebody will be able to be flown with a narrowbody at less risk from a capacity standpoint.

Victoria Moores and Alan Dron contributed to this report.

Aaron Karp