The Three-Tribe Format is a major tribe division twist that increases the number of competing tribes during the pre-merge phase of the game from two to three.
The idea behind the three-tribe format is to change up how the numbers work in the game. Whereas the basic two tribes can give one tribe an automatic numbers advantage, the extra tribe switches this up so that one specific tribe would have to get others on their side for a majority. Seasons with this format most commonly feature 18 castaways due to it being the most ideal number to still maintain equal numbers distribution. The downside to the three-tribe format means that the small numbers cause one tribe to fail more dramatically at the immunity challenges and lose a large chunk of their tribe. To stem this, a tribe switch usually dismantles one of the tribes, leaving the remaining two with mixed numbers from all three tribes. There have been variations to this. Second Chances introduced the Noonu tribe after a tribe swap, introducing the three-tribe format into the game after previously starting with the basic two tribes
The seventh season, Survivor: All Stars, was the first to feature the three-tribe format. It was brought in to complement the significance of it being an all-returnee cast for the first time.
Banaba Rawaki Vostok
The eleventh season, Survivor: Ethiopia, was the second to feature the three-tribe format. It divided the tribes of new castaways into two tribes from the beginning, by Brain vs. Brawn, but introduced a third tribe in a tribe switch.
Asosa Harar Maychew
The twelfth season, Survivor: Second Chances, was the third to feature the three-tribe format. It divided the tribes of all-returnee castaways into two tribes from the beginning, by random draw, but introduced a third tribe in a tribe switch.
Felidhu Mulaku Noonu
The fourteenth season, Survivor: Greece, was the fourth to feature the three-tribe format. It divided the castaways into three tribes from the beginning, based on what CBS Survivor season they said was their favorite on their application.
Boreas Eurus Notus
The fifteenth season, Survivor: Turkey, was the fifth to feature the three-tribe format. It divided the castaways into three tribes from the beginning, by Fans vs. Favorites vs. Friends.
Afyon Izmir Tokat