Hi Joaquin and welcome. It is actually a Gen 1.5, between gen1 and gen2. The "3.1" signifies updates to the original P365 design, including potential improvements to the trigger, slide, or other components, but not a complete redesign that would classify it as a new generation. Cheers and stay safe!

The SIG P365 9mm 3.1 Black 10RD Off Duty is considered to be part of the "first generation" of the P365 series, as the "3.1" designation refers to a later iteration of the original P365 design, not a new generation.