Abstract Klyuchevskoy Volcanic Group (KVG) is one of the world’s largest clusters of subduction‐zone volcanoes and hosts a complex trans‐crustal magmatic system. Using a machine‐learning–based detection workflow applied to data from the KISS seismic experiment in 2015–2016, we obtained an enhanced earthquake catalog for KVG volcano‐magmatic activity. Over 11,000 events were detected, approximately 14 times the number in the previous manual catalog, revealing seismicity strongly clustered in time and space and organized into localized bursts. Frequency index analysis and unsupervised clustering distinguish long‐period from volcano‐tectonic earthquakes. Long‐period events, associated with fluid and pressure changes, dominate the seismicity and span the crustal depth, forming deep‐to‐shallow conduits. Their frequency–magnitude patterns differ from typical tectonic earthquakes, highlighting volcanic source physics. Temporal changes in deep long‐period activity precede increases in shallow seismicity, consistent with magma or fluid pressure migration. Overall, our study reveals fine‐scale structure beneath KVG and provides insight into its multi‐volcano seismic processes.