Sony FE 100-400mm F4.5 GM OSS is a full-frame telephoto zoom lens with Sony E mount, part of the G Master series and designed for wildlife, bird photography, sports, action, photojournalism, and long-distance shooting. The 100-400 mm focal range allows users to work with distant subjects while maintaining good compositional flexibility, while the constant f/4.5 maximum aperture throughout the zoom range provides more consistent exposure handling compared with variable-aperture zoom lenses. The optical design uses ED XA, XA, Super ED, and ED elements, intended to control chromatic and spherical aberrations and maintain high-resolution rendering across the entire focal range. The autofocus system uses four XD Linear Motors and updated algorithms to handle moving subjects, with stated performance improvements over the previous FE 100-400mm F4.5-5.6 GM OSS. The internal zoom design helps maintain more stable lens balance during use, while Optical SteadyShot stabilization supports handheld shooting and dynamic shooting situations. The lens is compatible with Sony SEL14TC and SEL20TC teleconverters, allowing the focal range to be extended further when required. Sony FE 100-400mm F4.5 GM OSS is a professional solution for photographers and videographers looking for a super-telephoto zoom with constant aperture, advanced autofocus, G Master optical quality, and compatibility with the Sony full-frame mirrorless system.