As you can see from the announcement below, given to Vietnamese who receive a US visa, the US government is engaging in some low-key lobbying in an effort to persuade the Vietnamese government to bring the length of its visas into line with those of the US, i.e., from 3 months to one-year for business travelers and from one to three months to one-year for tourists. The implication is that if it doesn’t the US will decrease the duration of its visas for Vietnamese citizens. Will this effort succeed? If I were a betting man, I’d say “yes.”
My advice is to follow suit and also to increase the cost of a Vietnamese visa from $100 (single entry, one-month) to $160 so there is “fee reciprocity” as well. That’s being generous, considering that the U.S. per capita income (PPP) is 10X that of Vietnam.