FAST (Fully Automatic Spectrograph for Transient) has been designed to be a low-resolution spectrograph with multiple resolving power modes (R=60 and R=600 at 6500 angstrom) and covering a wavelength range between 3800A and 9200A. It includes also an imaging mode. The instrument will be installed at the PROMPT-7, a 32 inches aperture F/7 fully robotic telescope and located at Cerro Tololo Interamerican Observatory (CTIO). FAST will allow to efficiently obtain a first spectrum of transient events in the nearby universe, without human intervention, in a few minutes after their discovery. The project has just started the manufacturing and procurement phases. In this work we present the final optomechanical layout of FAST and we describe its development status.