Many have speculated whether North Korea’s claimed nuclear test test was a dud, a fizzle, or an outright fake. U.S. Intelligence officials confirmed that North Korea’s claimed nuclear test was indeed nuclear. Whether it was successful is another issue.
Officials said intelligence indicated the North Koreans predicted an explosion the equivalent of four kilotons of high explosives — but the test released less than one kiloton. (Source.)
From what I’ve read, four kilotons is a small nuclear device for a first attempt. For nukes, smaller is more difficult. Was North Korea attempting to make a smaller device that could be delivered by one of their missiles, or were they just trying to conserve their limited nuclear materials?