First tone. The fourth-tone 干饭 is recent internet slang for tucking into a meal and is a different word with a different traditional form, 幹飯 against 乾飯 for the rice.
usage
This is the older, everyday word, and it exists mainly as the opposite of 稀饭 or 粥. It is heard most in the southwest, where a meal is described by which of the two you are having.
