Radiance Simulator v2.1 has been released. The main new features are: support for RTTOV v12.2, temporal interpolation of model data to observation times, optional use of RTTOV parallel interfaces for multi-threaded simulations, more RTTOV options can be specified in the configuration file, output files now use netCDF-4 classic format with internal compression, and a new Python script which can be used to create configuration namelists and run RadSim from the command line.