ALICE (A Large Ion Collider Experiment), an experiment optimized for the study of heavy-ion physics at the Large Hadron Collider (LHC), has delivered a wealth of important physics results during Runs 1 and 2 of the LHC. In order to profit from LHC luminosity increases and advancements in detector technology, the ALICE experiment underwent a major upgrade during LHC Long Shutdown 2 (2019–2022). This includes a comprehensive upgrade to the core detectors and a new event processing infrastructure with a redesigned online–offline software framework. These improvements enable the recording of Pb–Pb collisions at interaction rates of up to 50 kHz with a continuous readout.

ALICE has been operational and collecting data since the start of LHC Run 3 on July 5$^\mathrm{th}$, 2022. In this paper, the ALICE upgrade during the Long Shutdown 2 will be described briefly. Preliminary performance results of the upgraded detectors from the first phase of proton–proton and Pb–Pb collisions in the LHC Run 3 will be discussed in detail.