Welded hollow section trusses are commonly used in structures such as pedestrian bridges and crane girders. High‐strength steels (HSS) enable increased load capacity and reduced weight, but their limited ductility restricts plastic stress redistribution, which is typically assumed in current design rules for mild‐strength steels (MSS) to mitigate local stress concentrations. To account for the reduced ductility of HSS, reduction factors are applied to the design rules for MSS for steel grades above S355. However, these factors are overly conservative and insufficiently calibrated due to limited experimental data on HSS joints. This article presents an experimental and numerical study on K‐joints made from circular and square hollow sections of HSS, aiming to reassess the existing material reduction factors. Damage mechanics‐based material models calibrated through extensive testing are used in finite element simulations to capture joint behaviour up to failure. The numerical models are validated against large‐scale tests on HSS K‐joints. The present study includes 19 experimentally and 580 numerically investigated joint configurations, mainly made of S460NH and S620QH. Key findings include the consistent occurrence of punching shear failure as the decisive failure mode. While current design rules lead to mostly safe structural designs, differentiating reduction factors considering the failure mode and steel grade could enable a more efficient and material‐optimised design of HSS joints.