The T'au were eventually modified to display the same altruistic overtones, but with a heavier Orwellian tone that implies that the T'au engage in mind-control and population replacement on worlds within their domain. This development was eventually seen as too disparate from the traditional dystopic atmosphere of the rest of the setting. ДЄccording to Andy Chambers, the chief designer at the time, the T'au were intended 'to be altruistic and idealistic, believing heartily in unification as the way forward.' Graham McNeill was responsible for much of the background material produced for the T'au, developing what Andy Chambers described as 'their proud, quiet but determined character to the point where they actually became a rather likeable, if slightly naive addition to the cosmos.' The Kroot were originally conceived as a separate army in themselves, but were eventually merged with the Tau. This idea was proposed by Jes Goodwin, who is a sculptor at Games Workshop, as a way to attract new players who weren't interested by the overall fantasy-in-space theme of the other Warhammer 40,000 races. the Eldar are based on High Elves), the culture and technology of the Tau were heavily inspired by Japanese science-fiction. Whereas most of the races in Warhammer 40,000 are based on Tolkien fantasy races (e.g.

The Spirit caste was renamed 'Ethereal', and the Ethereals became non-psychic so as to differentiate them from the Eldar Seer councils. The caste system became part of the new Tau race. In 1999, Thorpe revisited his Shishell concept when Games Workshop asked him to develop a new army. The race was ruled by a caste of psykers. The Shishell had five castes: Earth, Air, Fire, Water, and Spirit. Like the Lizardmen, the Shishell had a caste-based society. Initially, he conceived them as the counterpart to the Lizardmen faction from Warhammer Fantasy, in the same way the Eldar are the counterpart of the High Elves, and he called them 'the Shishell'. Gavin Thorpe began developing what eventually became the Tau in the early 1990s. Kroot warriors provide melee support, while the insectoid Vespids serve as jump infantry. The Tau are the only army in the game that routinely incorporates aliens from other species. AI drones act in a support role, offering fire support, specialized equipment, laser guidance, or physical protection for manned units. The bulk of their heavier units are made up of battlesuits which act as mobile heavy weapons platforms piloted by single soldiers. Most T'au vehicles have the 'Fly' keyword, allowing them to move over terrain without issue.

There are, however, optional rules in the Open Play format for including psyker auxiliaries from other races as well as Relics for use in Narrative Play that allow models to counter psychic powers. The T'au do not have any psykers nor units that specialize in countering psykers, which makes them somewhat more vulnerable to psychic attacks.

While most armies in 40k may only make a single overwatch action a turn, Tau have no such limitation, and may even have units fire overwatch for close by allies. They heavily use the Overwatch special rule, which allows them to shoot back at their enemies when charged, with devastating power. They have some of the most powerful ranged weaponry in the game in terms of both range and stopping power. The T'au specialized in ranged warfare and die quickly in melee. Warhammer 40,000 game mechanics (as of 9th Edition) 2.2 Influence of the Eye of Terror campaign.1 Warhammer 40,000 game mechanics (as of 9th Edition).

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