From 30 Aug 2016, based on an agreement between Vietnam and US government.
Vietnam will issue multiple-entry visas valid for up to one year to U.S. citizens who wish to travel for short-term business or tourism and who otherwise meet the requirements to enter Vietnam.
The new visa rule will “benefit American and Vietnamese tourists and business travelers, generating new opportunities for trade, investment and tourism,” the U.S. Embassy in Hanoi commented.
The previous maximum validity for Vietnamese visas issued for these purposes was, in most cases, three months with just a single entry.
Other types of Vietnam Visa ( 1, 3 month single or multiple entry) are NO more available for US passport holders or will be automatically changed accordingly.
The service fee for 1 year multi-entry visa is 30 USD and stamping fee is 135 USD for each person.