GenX fibers are the newest series of Large Mode Area (LMA) double-clad fibers, specifically tailored to enable power scaling of multi-kW -class fiber lasers and amplifiers. Offering superior photo-darkening (PD) performances with maintained and/or higher absorption, these fibers are optimized to benefit both CW and pulsed multi-kW systems. The 14/250 GenX design is ideal for efficient and reliable kW-class systems. The 20/400 GenX offers the same absorption with significantly lower PD than comparable products providing an optimized platform for high efficiency and high-reliability multi-kW CW lasers. The 25/250 GenX product combines higher absorption and superior PD, ideal for enabling multi-kW peak power scaling with reduced cavity length and nonlinearities.