There are two (or three, it is rumored) castes of Dwarves.

Stone Dwarves are much like the PHB dwarves, adjusting for local culture.

Clay dwarves, however, are new.

Clay Dwarves:

Short lived and (especially to a dwarf) freakishly thin. They are like dwarves on overdrive; the mature about twice as fast as a human. By age two, clay dwarves have enough cunning to survive even in harsh conditions. In the Iron Empire, they are sent to "the boards", a kind of communal fostering home. By age five [about as mature as a 10 year old human] they are sent out with the army as hole diggers, water fetchers, etc. Around age eight they are given weapons and fight with the unit. Sometime around age 10 they reach their intellectual peak (though their studies are mostly war and survival rather than book learning.)

Lucky clay dwarves continue fighting until they wear out around at about 15 to 20, or until they pick up a maiming injury. When they are retired (often to the northlands), they return to fetching, carrying, farming, herding, and chopping. In rare cases, clay dwarves will live as long as 40 years, though they are usually abandoned earlier, when their usefulness has run out.

Clay dwarf names are cut down versions of regular dwarf names, so Jol or Dorf instead of Skjoldorf, Rik instead or Rorik, etc. They are not acknowledged by their kin and have no family names.

Skin is gray rather than slate, marble, or obsidian

They are skinny and slightly shorter than Stone Dwarves

They are weak but fast, and despised by dwarf and non-dwarf alike

- -2 strength, -2 Charisma, +2 Dexterity

- Small size: +1 bonus to Armor Class, +1 bonus on attack rolls, +4 bonus on Hide checks, -4 penalty on grapple checks, lifting and carrying limits ¾ those of Medium characters.

- A clay dwarf's base land speed is 30 feet.

- Darkvision out to 60 feet.

- +4 racial bonus on Move Silently and Ride checks

King's Clan:

The King's clan is rumored to have driven themselves insane due to their experiments with necromancy, demon summoning, and infernal pacts.  They might be simple Deep Dwarves or they may be twisted Duergar by now.