My sandbox for Call of Duty: Mobile
How to identify SIG MPX generations
The differences are circled in red:
The production versions of the MPX SMG/SBR have a default barrel length of 8" (with 6.5" being an optional one), whereas the prototype counterparts were shown with a 6.5" barrel.
Regarding the external differences of the Gen 1 vs. Gen 2, the different ejection port and the scalloped top rail are definitive characteristics of an MPX Gen 2. This version also has by default an ambidextrous charging handle and a KeyMod handguard, though some MPXes Gen 1 could also be seen with them. For more details about Gen 1 vs. Gen 2, there is an article here.
After Gen 2, the MPX gradually went through some redesigns. The current production version has a narrower plate on the left side of the upper receiver, no "SIG MPX" markings next to it, an M-LOK handguard, two less diagonal vents above it, and a redesigned area around the magazine release. It is also commonly seen with a Timney trigger. This version is often colloquially referred to as "Gen 3" on the internet, though SIG Sauer doesn't seem call it like that.
Table of Glock models