According to the U.S. Hemp Farming Act of 2018, any constituent of the hemp plant is legal as long as it contains less than 0.3% Delta 9 THC on a dry weight basis. It doesn’t make any delineation about Delta 8 specifically. So, at the federal level Delta 8 THC is legal.
However, some states in the U.S. aren’t permitting the sale of Delta 8 products. Be sure to look up the local laws in your state before you buy.