Operational experience with the new ATLAS HLT framework for LHC Run 3

Athena is the software framework used in the ATLAS experiment throughout the data processing path, from the software trigger system through offline event reconstruction to physics analysis. For Run 3 data taking (which started in 2022) the framework has been reimplemented into a multi-threaded framework. In addition to having to be remodelled to work in this new framework, the ATLAS High Level Trigger (HLT) system has also been updated to rely on common solutions between online and offline software to a greater extent than in Run 2 (data taking between 2015-2018). We present the now operational new HLT system, reporting on how the system was tested, commissioned and optimised. In addition, we show developments that have been made in tools that are used to monitor and configure the HLT, some of which are designed from scratch for Run 3.