The public debut of the stretched and re-engined single-aisle keeps the programme on track for first flight in April followed by entry into service in 2018.
The 737 Max 9 is 42.1m (138ft) long, a 2.6m stretch of the 737 Max 8.
Boeing also is gauging airline interest in a 1.68m stretch of the 737 Max 9, which has sold poorly compared to the Airbus A321neo.
The CFM International Leap-1B-powered 737 Max family has picked up more than 3,600 orders overall, but only about 220 for the 737 Max 9.
Meanwhile, Boeing is preparing the 737 Max 8 to enter service as early as April with launch operator Norwegian.