In Civilization VI, a unique unit is a special unit that is only available to a specific civilization (once they discover the appropriate technology or civic, of course). Some leaders also have abilities that give them access to a unique unit, in which case the player can have two unique units (e.g. when playing as Teddy Roosevelt in vanilla Civilization VI, or as Rough Rider Teddy with the Persona Packs enabled). All unique units have historical connections to their civilization and/or leader - their names and models, and in some instances their special abilities, are based on these connections.
Unique units have special advantages that make them superior to standard units. These can comprise higher base stats (higher Combat Strength or Ranged Strength, more Movement, etc.), and/or special abilities that are truly unique (such as the Canadian Mountie's ability to establish National Parks). Prior to Gathering Storm they also don't require strategic resources to train. In Gathering Storm all unique units require resources to train and maintain (unless they replace a standard unit that doesn't require strategic resources itself), but they always require smaller amounts of resources than their common counterparts.
Unlike in previous Civilization games, unique units do not always replace standard units. When they don't, they often fill a niche for each player that no other civilization/leader can fill at the time, giving that player a distinct advantage over his or her rivals. However, these standalone unique units cannot be pre-built and upgraded into, so they require more Production investment. Note that unique units may belong to different eras than those they replace, which is important when considering era-specific policy cards or the effects of Great Generals and Great Admirals.
There are rare instances in which a unique unit of one civilization can be controlled by another one:
- Genghis Khan has a chance to capture unique cavalry units when he defeats them with his own cavalry units.
- The Sea Dog can capture unique naval units when it defeats one.
- A civilization that levies the army of a city-state can upgrade its levied units into their unique units. These unique units retain their unique identity when the city-state regains control of them, and can be levied by another civilization that becomes the Suzerain of that city-state.
- In Heroes & Legends, Hunahpu & Xbalanque can resurrect defeated unique units to fight under new leadership.
- In Barbarian Clans, Barbarian camps can train unique units of other civilizations who are not present in the game, which can then be hired by any major civilization at a Gold cost.
Despite all of these instances, there is currently no special ability or method that can be employed for a civilization to build another civilization's unique unit from scratch.