The cimbasso is an orchestra brass musical instrument and is part of the low brass family, covering the same range as the tuba or contrabass trombone; most often pitched at F.
In short, no; the cimbasso is not a transposing instrument.
The cimbasso was originally an Italian instrument specified by Verdi and other Italian opera composers to be used as the bass voice for the brass in the orchestra instead of a tuba.
