According to Marvel, the series is 'officially' considered part of Earth 616 continuity, however many fans consider it to be a parallel universe story as there are numerous continuity errors.
Collected EditionsX-Men: First Class - Mutant Mayhem (#1-5)X-Men: First Class - Road Trips (#1-9)X-Men: First Class: Band of Brothers (#6-10)X-Men: First Class: The Wonder Years (#11-16)Translated into Spanish.
— Description from Comic Vine community (comicvine.gamespot.com · https://comicvine.gamespot.com/x-men-first-class/4050-18941/).
