The Mercedes-Benz GLS (Generation X166) is not an entirely new model, but a deep facelift of the GL (X166) launched in 2012. This nomenclature change at the end of 2015 aimed to align it with the S-Class, officially positioning it as the "S-Class of SUVs". It is a luxurious behemoth measuring over 5.10 meters and offering 7 real seats. While the ride comfort (thanks to the standard AIRMATIC air suspension) and soundproofing are imperial, this flagship requires a maintenance budget commensurate with its badge. In terms of reliability, the record is mixed: the V6 petrol engines are robust, but the V8s (M278/M157) suffer from costly design flaws, and the onboard electronics as well as the air suspension sometimes age poorly.
The Mercedes GLS X166 is a formidable travel machine, but it represents a significant financial risk on the used market if chosen poorly. If you are looking for a petrol model, the GLS 400 / 450 (V6 M276) is by far the most rational and reliable choice. The V8 versions (GLS 500/550 and AMG 63) are to be avoided unless you have a substantial repair budget and have had the cylinders inspected by a professional before purchase. The diesel (GLS 350 d) remains relevant for high-mileage drivers, provided you check for the absence of leaks at the oil cooler. In all cases, plan for a large annual budget for routine maintenance and the inevitable quirks of the air suspension.