>>1388533Prime 9 chains have internal dimensions that are compatible with modern Wide / Narrow chainrings and similar chain retention to 11 / 1 2 speed chains. Externally, Prime 9 chains have dimensions similar to existing 9-speed chains. This unique geometry allows for thicker side plates than 12-speed drivetrains which resists stretching over time, increasing shifting performance while decreasing wear on the cassette and chainring.
There is no "narrow wide chain". They're just saying that their 9 speed is compatible with the modern narrow/wide chainrings that are ubiquitous in the mtb world. I bet a run of the mill 8/9 speed chain would work just fine.
