The temporary Extended Pollino Seismic Experiment (FDSN network code Y4) monitored the earthquake swarm in the Pollino Range region, Italy, between September 2014 and April 2015. The experiment followed the Pollino Seismic Experiment, 2012-2014 (network code: 4A) [1] in the same area, further enhancing the detection and analysis capabilities there. It was part of a collaborative effort made by the German Research Centre for Geoscience (GFZ) and the Istituto Nazionale di Geofisica e Vulcanologia (INGV) within the CCMP-Pompei, FEFI and NERA projects. The Pollino Range region is located at the transition from the Southern Apennines chain to the Calabrian arc. Striking a volume of about 20x20x15 km, the swarm started in October 2010, culminated in a Mw=5.2 on 25 October 2012 and has continued since with a variable rate of activity. The area represents a seismic gap as there are no documented historical M>6 earthquakes during the last thousand years. The tectonic structures of the area are poorly known. The Y4 network consisted of 19 stations including 14 broadband and five short-period instruments. All instruments were provided by the Geophysical Instrument Pool Potsdam (GIPP) and the CCMP-Pompei project at GFZ and INGV. They were complemented by another four temporary IV stations installed by INGV. The short-period stations had Mark L-4C3D sensors with EDR digitizers. The broadband stations were equipped with STS2.5 seismometers and RefTek RT130S digitizers or Güralp CMG-ESP or Güralp CMG-40T seismometers and EDR digitizers. Eleven broadband (CSA0 to CSA10) were installed in a small-aperture detection array in the west of the range. The other 8 stations (broadband: CSB, CSE, CSD0 and short period: CSF, CSG, CSH, CSI, CSK) formed a network in the swarm area. The array and the network stations recorded in continuous mode at 200 Hz. The sensors were buried in the ground at 0.5 m depth except for CSB, CSE and CSD0 which were installed on the surface. High-precision station coordinates were obtained by using differential GPS measurements. The data have been used to analyze the earthquakes and seismogenetic structures and to discern the characteristics of the swarm sequence. Waveform data will be fully open after April 2017. [1] Pollino Seismic Experiment, 2012-2014, doi:10.14470/9N904956