A highly-advanced weapon, it is a laser rifle, and serves as the primary assault weapon of STAG. As such, it can aquired by killing or disarming them with the Human Shield. By default, the Viper fires somewhat sluggishly, but deals reasonable damage; It has better accuracy than the K-8 Krukov and deals more damage as well (though it is less damaging and less accurate than the AR-55. As an energy weapon, the Viper has no need for magazines and can continue firing as long as there is ammunition for it, though it's necessary to carefully control the firing rate to avoid excessive heat buildup. If the weapon overheats, it is rendered inoperative until it fully cools down.
The Viper gets considerably better with upgrades, which improve its accuracy and dramatically improves its fire rate. Fully upgraded, the Viper strikes a perfect balance between the speed of the K-8 Krukov and power of the AR-55, making it an excellent weapon for most combat situations, though it loses out to the other rifles on some category or another: The K-8 fires quicker and can rack damage up quicker as a result, the AR-55 and TOGO-13 do more damage and have better accuracy, and all of the above weapons are magazine-fed, which makes them much quicker to get back into the fight after spending a magazine than the Viper does after overheating.
Jenny Jaros carries a Viper Laser Rifle whenever the player calls her as a homie. If the Gangstas in Space (DLC) is completed before the STAG arc of the storyline, it might be possible to acquire the Viper early by calling Jenny up, killing her, and taking the weapon from her corpse.
The Viper is the only weapon featured in the mission "Gangstas in Space". During the mission, it is fully upgraded, though it loses the upgrades after the mission is complete.
The Viper is similar in appearance to the Nerf Longstrike, a dart blaster. They feature a similar straight-panel barrel and thumbhole stock.
The unlimited clip cheat doesn't work with the Viper Laser Rifle, due to it being an energy weapon. Therefore, it doesn't utilize usage of clips (magazines), but instead, the heat system serving as the replacement.
Despite using a laser technology, the damage-bullet 4 upgrade protects against it, the same goes with the s3x shotgun.