Apex Legends data miners have found two weapons that might arrive in the upcoming Season 4.
Given that developer Respawn Entertainment has previously added one weapon each to the assault rifle, LMG and sniper rifle weapon categories, SMGs and shotguns seem the most likely to receive new additions. Both the weapons discovered by data miners are submachine guns.
The first of the two weapons is the Volt, discovered in the Apex Legends files in September by That1MiningGuy. The Volt appeared in Titanfall 2, as did many of the other weapons that have since been added to Apex Legends. Titanfall 2 described it as firing "concentrated bolts of high energy," suggesting it would also be an energy weapon in Apex Legends. If that were true, it would be the first energy SMG after the assault rifle, LMG and snipe rifle weapon types each received their own.
In Titanfall 2, the Volt had a lower fire rate, damage, and time-to-kill than the R-97 — Titanfall's version of the R-99. To compensate, the Volt sported higher accuracy and longer range.
The second SMG option is the CAR, discovered in the files by That1MiningGuy in July. The Titanfall version of the CAR had relatively high per-bullet damage and accuracy, but a lower fire rate and shorter magazine. It fired traditional bullets rather than energy.
Respawn Entertainment may have teased the introduction of the CAR at TwitchCon 2019, where an official Caustic cosplayer was spotted carrying a replica of the gun.
Although these appear to be the most likely options, it's possible neither will be Season 4's new weapon. Respawn Entertainment has yet to confirm any information about the upcoming season beyond its Feb. 4 start date.