The Ferrari-powered U.S.-owned team, who finished eighth overall last season for the second year running, released digital images of the VF-18 car on their website and social media.
"The biggest part of the car’s evolution was the addition of the halo," said team principal Guenther Steiner in a statement.
"It took quite a bit of study by the aerodynamicists, but the designers had to work hard to modify the chassis so the halo could survive the mandated loads."
The halo, fixed at three points with its central upright in front of the driver and an overhead loop, is designed to protect the otherwise exposed helmet from bouncing wheels and flying debris.
The Mercedes team's technical head James Allison said last week that the device can withstand the weight of a London double-decker bus.
With few other rule changes for 2018, Steiner said the car was "less about reinvention and more about refinement.
"You see elements we had from last year on the car this year," he added.
"Our 2017 car was actually pretty good, but we didn’t always get the best out of it, and that’s what we aimed to change in 2018. We got the car as light as possible to carry more ballast. We were able to do a better job of putting the weight where we wanted it."
Testing starts in Barcelona on Feb. 26, with Frenchman Romain Grosjean and Denmark's Kevin Magnussen returning as Haas's line-up for 2018. The season-opening race is in Australia on March 25.
Williams are due to unveil their new car on Thursday with the remaining teams holding launches, virtual and real, during the course of next week.
Champions Mercedes, with Britain's Lewis Hamilton going for his fifth title this season, will present their car at Silverstone on Feb. 22.
(Reporting by Alan Baldwin, editing by Toby Davis)
