Borderlands 3 guide: When do you get new weapon slots?

You summon Iron Cub equipped with duplicate weapons from the remaining skill slot Iron Cub follows you and attacks nearby enemies dealing reduced damage

Weapon Trinket, 4th Weapon slot Unlock, Unique Legendary SMG Go to Sanctuary bridge, Eliminate Maliwan squad Upon completing the previous mission

borderlands 3 artifact slot unlock Borderlands 2 - Ulitmate Guide to Slots

borderlands 3 unlock artifact slot Your 4th Weapon Slot will unlock after completing the first vault mission in the main story, Beneath the Meridian, which is the 10th main