The Boeing 787-8 was the first 787 variant to enter commercial service.
The 787-8 is the original production version of Boeing’s Dreamliner family. It was developed as a midsize, long-range wide-body aircraft using extensive carbon-fiber composite structures, larger windows, and systems intended to improve fuel efficiency and passenger comfort.
After a lengthy development program, the 787-8 entered commercial service with All Nippon Airways in October 2011. Later versions extended the family: the 787-9 added fuselage length and range, while the 787-10 became longer but sacrificed some range for additional seating capacity.
The 787-3 was proposed as a shorter-range, high-capacity version for Japanese domestic operations, but it was never produced. Therefore, the 787-8 is the correct answer rather than the later -9 or -10.