The validity of Form W-8 depends on the type of form being filled out. Generally, Form W-8BEN and W-8BEN-E remain valid for three years after the date it was signed, while a Form W-8EXP and W-8IMY remain valid for one year after the date it was signed. This means that if an individual or entity wishes to maintain their foreign status with the IRS, they should ensure that they renew their forms before these timeframes are up.