Starliner's astronauts will spend at least 8 months in space, longer than a typical ISS crew. But numerous other astronauts have safely spent a year on the ISS, or even longer.

Boeing Starliner astronauts have years of medical studies helping them with longer stay in space

Source: space
Source Link: https://www.space.com/boeing-starliner-astronauts-medical-studies-long-stay