The Ø10.4 m × 5.7 m EGL (effective grinding length), 11 MW semi-autogenous grinding (SAG) mill at Harmony Gold Mining’s Hidden Valley operation has undergone several liner design and operating strategy changes over its operating life. With Harmony’s strong focus on operational excellence and continuous improvement, one of the key areas of collaboration with Metso was mill lining design. A drive for improved throughput, milling efficiency, and maintenance practices has resulted in a high level of optimisation and innovation. Structural foundation concerns placed significant constraints on the mill system weight and necessitated strict control of operating speed. A heavy lining system and suboptimal mass distribution limited available operational charge mass and constrained mill performance. Various developments and innovations were undertaken by Harmony and Metso over the years to alleviate these issues and improve performance. In 2013, development efforts focused on increasing throughput by optimising the discharge system. Grate wall improvements, using Metso Poly-Met™, aimed to eliminate pegging and increase open area to an optimal level. A pulp discharge system upgrade also improved volumetric discharge capacity. The use of rubber and composite components, rather than metallic, has allowed a reduction in system weight and helped overcome charge mass limitations as described above. In 2015, mill efficiency was improved through optimised charge motion following the introduction of a skip-row shell lining utilising Poly-Met™. This design delivered higher milling efficiencies with an improved transfer of mill motor power to size reduction and eliminated packing events. Although throughput was improved and liner life was stretched to greater than nine months, additional optimisation opportunities presented. Long-term operational data analysis of the updated design showed a significant improvement in mill performance following a shell reline, however a decrease in milling rates and efficiency was consistently observed after approximately six months of operation. An updated strategy was the natural next step. With Harmony’s strong focus on operational excellence and milling efficiency, the latest Megaliner™ design iteration, with a substantial reduction in pieces and improvement in fastening system, has adopted a whole-of-plant value and performance philosophy and is configured to allow quicker relines. This enables a higher reline frequency with minimal impact on annual downtime and takes advantage of the higher throughput state in the early stages of liner life. This paper demonstrates the history and key operational data following the various optimisations and innovations that have improved SAG mill performance at Hidden Valley since 2013, with particular emphasis on the most recent innovations delivering faster, safer and more efficient relines.