The lightweight belt is currently vacant because Islam Makhachev vacated it in 2025 to move up to the welterweight division. Makhachev, who had a record number of consecutive lightweight title defenses, relinquished the belt to pursue a title at welterweight, leading to the lightweight championship being open for contenders like Ilia Topuria and Charles Oliveira to fight for it at UFC 317. This move was partly influenced by the UFC's stance against fighters holding two belts simultaneously and Makhachev's relatively low fight activity at lightweight, which made holding two titles impractical.

Previously, the belt had also been vacated when Charles Oliveira was stripped for missing weight at UFC 274, but the current vacancy is due to Makhachev's move to a higher weight class.

In summary, the lightweight belt is vacant mainly due to Islam Makhachev vacating the title to compete at welterweight.