  We present the performance of the upGREAT heterodyne array receivers on the
SOFIA telescope after several years of operations. This instrument is a
multi-pixel high resolution (R > 10^7) spectrometer for the Stratospheric
Observatory for Far-Infrared Astronomy (SOFIA). The receivers use 7-pixel
subarrays configured in a hexagonal layout around a central pixel. The low
frequency array receiver (LFA) has 2x7 pixels (dual polarization), and
presently covers the 1.83-2.06 THz frequency range, which allows to observe the
[CII] and [OI] lines at 158 um and 145 um wavelengths. The high frequency array
(HFA) covers the [OI] line at 63 um and is equipped with one polarization at
the moment (7 pixels, which can be upgraded in the near future with a second
polarization array). The 4.7 THz array has successfully flown using two
separate quantum-cascade laser local oscillators from two different groups.
NASA completed the development, integration and testing of a dual-channel
closed-cycle cryocooler system, with two independently operable He compressors,
aboard SOFIA in early 2017 and since then, both arrays can be operated in
parallel using a frequency separating dichroic mirror. This configuration is
now the prime GREAT configuration and has been added to SOFIA's instrument
suite since observing cycle 6.
