Transition metal nitride coatings often face a trade-off between thermal stability and oxidation resistance at high temperatures. Here, we address this challenge using a mechanism-guided high-throughput combinatorial strategy, implemented through multi-target co-deposition, to rapidly probe the Al-Cr-Ti-Si-N compositional space. An optimal composition window was identified (Al 13.3-24.1 at.%, Cr 7.6-14.6 at.%, Ti 10.4-23.9 at.%, Si 1.3-3.2 at.%). Coatings within this window exhibit high hardness