This is a genuine AAM rear axle shaft for the 11.5 rear axle found in many 2011-2018 GM trucks. This axle has 30 splines. Here is the information from AAM’s website:
40097464 | GM | Sierra, Silverado, | 2014 – 2018 | 11.5″ 14 Bolt – Rear Axle | L/R DRW – NT | 30 spline | 943MM | with VSES |