Yamaha's professional Bb horns (since the introduction of the heavywall horns) have been designated with a series of 3's (x335) and C trumpets with a series of 4's (x445)

6335HSII was the Bb Heavywall (predecessor to the Xeno)
6345HSII was the large bore version
6445 was the C version

... exact same thing for the Xenos

8335(G, RG) have all been ML Bb horns with the 8345's all being large bore
8445 being the C version

the same continues to hold true with the Artist series
9335 are Bb horns and 9445 are C horns

The Artist model Chicago C trumpet is the only C trumpet that Yamaha produces with a reverse leadpipe (Malone MC2)