"Biohazard 3.5" or "Resident Evil 3.5" are informal terms used to describe the various prototype stages of development of resident evil 4 (biohazard 4). Officially announced in 2001, Resident Evil 4 underwent a long development period in which three proposed versions of the game were discarded by the developers before the finished product was released in 2005. An earlier game, also known as RESIDENT EVIL 4, was in production until 2000 but was led by an unrelated design team.