The ISO B hub was originally called the ISO SD hub, and is actually still available with 100mm axles, as shown in the photos. It uses smaller diameter bearings, and is convertible between 100x15mm, 100x12mm, and 110x15mm thru axle configurations as well as a 100x9mm quick release axle. This hub comes standard with Chris King's legendary bearings that carry a lifetime warranty, but is also available with a ceramic bearing upgrade. Finally and importantly it's set to be discontinued in the near future.
The ISO AB hub can really be thought-of as the next-generation of Chris King front mountain bike hubs: it's boost-only, and is convertible between 110x15mm, and 110x20mm boost thru axle configurations. The bearings and the basic hub design are an evolution of Chris King's LD hub, so they are built to handle abuse without weighing a ton. It's also available with 110x15mm torque caps for some Rockshox forks. Like the ISO B, the ISO AB hub is available with either standard bearings or the ceramic bearing upgrade.
This is the hub that we recommend to most riders because it's tough, fits all current standards, and is designed to be as future-proof as possible, but for those riders looking for a shapely hub that will fit their 100mm fork, the ISO B is worth considering while it's still available.