From Halopedia, the Halo wiki
The Evo Holopoint, sometimes shortened and stylized as EVO, is a telescopic sight commonly mounted on the M392 Bandit. The optic is capable of 1.6x magnification and includes an ammunition counter to inform the user of how many bullets remain in the magazine as they are aiming down the sight.
Following the introduction of the M392 Bandit into Halo Infinite with Season 03: Echoes Within, 343 Industries felt that the weapon required further tweaking in order for it to become a starting weapon in competitive modes. This inspired the creation of the Bandit Evo and the Evo Holopoint sight itself.