The official currency in Laos is the Lao Kip (LAK); and 1 USD is equivalent to 9,517.08 kip (as of 19th July 2021). LAK is the most commonly used, but US dollars and Thai Baht are also acceptable in popular tourist cities and towns, such as Luang Prabang and Vientiane. If you make smaller purchases, LAK would be expected.
Credit cards are also acceptable in airports, major hotels and shopping malls, etc.