Fastbacks are known for a single slope from the roof to the rear of the vehicle, as seen on the rival Ford Mustang.
The new 408 is much lower and longer than Peugeot's 3008 SUV, with a flowing and aerodynamic line giving it a distinctive silhouette that sets it apart from mainstream models.
However, the new car, which will be built in Mulhouse, eastern France, does have some popular SUV characteristics such as a high ground clearance, big wheels and black plastic cladding on the fenders, sides and back of the compact.
The 408 will have its public debut at the Paris auto show in October. It will be launched early next year in Europe and will go on sale by mid-2023 in China, where it will be built in Chengdu.
It will initially be equipped with gasoline and gasoline-electric hybrid powertrains before switching to a full-electric version.