They are called Stretched Variant and Shortened
In China, at the Shanghai Aerospace Exhibition, COMAC Corporation presented new versions of its C919 medium-range aircraft: Stretched Variant and Shortened Variant. In fact, the first will be an analogue of the Airbus A321, and the second will be an analogue of the Airbus A319.
If the standard COMAC C919 in a two-class layout for China Eastern Airlines can accommodate 164 passengers, then the “stretched” version can accommodate 210 passengers in a two-class layout. That is, it will reach the level of the Russian MS-21.
The shortened version will accommodate 140 passengers, but it has an important mission: this version can be used at all high-altitude airports in China.
China is the world leader in the number of high-altitude airports: 20 of the country's air harbors are located at altitudes from 1524 to 2438 m, another 23 airports were built at altitudes above 2438 meters. And the highest airport (in Sichuan province) is located at an altitude of 4411 meters.
There are no technical details about the new versions of the COMAC C919 – these options are still in the early stages of design.