What is the difference between alprazolam and diazepam?

Lasting. Alprazolam is fast acting benzodiazepine and diazepan is a long acting one. First one like 3 hours and the later one 12 hours mor or less depending on patient health status and metabolism.
Length of action. Alprazolam (xanax) & diazepam (valium) both belong to a family of anxiety meds called benzodiazepines. Alprazolam is relatively short-acting (less than 24 hrs) & diazepam is long-acting (more than 100 hrs). Diazepam is also used as a muscle relaxer and for certain types of seizures. Alprazolam is considered to have more addictive potential than diazepam but both must be used with caution.