Intel stopped putting an i in its processor names when the Core Ultra brand arrived. The last Core i9 mobile parts belonged to the 14th generation, and everything at the top of the stack since then carries Core Ultra 9 on the badge. Searching for a Core i9 Lenovo lands you on Core Ultra 9 machines, which are the direct successor.

Two very different chips share that tier. HX parts are cut from desktop silicon, run at high sustained wattage and take replaceable DDR5 modules, which is what sits inside Legion and Legion Pro gaming machines. H-class and X-class parts are thinner-chassis designs with a larger integrated Arc graphics allocation, used in Yoga and ThinkPad flagships.

Which one you need follows from the graphics card rather than the processor badge. A Legion with an HX chip exists to feed a discrete NVIDIA GPU; a Yoga with an H-class chip exists to last a working day on battery.