A go apprentice (insei (院生 insei) is a student learning to play Go at an institution, typically with the aim of becoming a professional player. In Japan, such a student is called an insei (literally, "institution student"). Institutions for insei include the Nihon Ki-in (Japanese Go Association) and the Kansai Ki-in (Kansai Go Association). The equivalent of Go insei in Korea is "Yeon'gusaeng" (Hangul: 연구생; hanja: 硏究生; RR: Yeon(-)gusaeng), read "kenkyūsei" in Japanese and "yán jiū shēng" (also meaning "graduate student") in Chinese.
In Japan, once a year 3 or 4 apprentices who qualify in a yearly tournament become professional players.
Asian players are required to become a professional before the age of 18 while studying as insei, but foreigners have the chance up to the age of about 30.
To become an insei, a person requires a professional to sponsor them, and an application to the Nihon Ki-in. There is no official way to contact a professional for sponsorship.
While insei, many people live with their professional sponsor, who tutors and supports them. Some insei just visit their professional sponsor several times a week. The professional sponsor acts as a mentor for the insei.