BMW says the Gran Coupe is a 4 +1 seater (compared to the 2 +2 Coupe), meaning that it will comfortably seat four people and can accommodate a fifth passenger between the rear bucket - like chairs for short journeys. (evo.co.uk)
Space is good for four adults, with ample leg - and headroom in the back seats, though a fifth passenger will be a squeeze. (evo.co.uk)
In the back, seating is very comfortable for a pair of six - footers, and enough room for a fifth passenger to not feel claustrophobic. (automobilemag.com)