Supernovae and kilonovae are transients resulting from the collapse of massive stars, and the merger of two neutron stars, respectively. Together they produce most of the elements in the periodic table, and probe astrophysics in its most extreme regimes. This project carries out simulation work for two projects: 1) The Swedish Research Council project 2018-03799 "Supernova and kilonova explosioner: diagnostisering av Universums ämnesfabriker", and 2) The Knut and Alice Wallenberg Foundation project "Gravity Meets Light". Our research group is developing and applying state-of-the-art spectral models for these astrophysical explosions, considering the key physical processes to a high degree of realism including sophisticated radiative transfer. These models can be used to analyse observed spectra of supernovae and kilonovae, and from those comparisons we can infer important properties such as which elements are produced in which explosions, what is the mass and velocity of the expanding debris, and what is the nature of the compact objects (neutron stars and black holes) left behind. The physical modelling involves solving the energy equation, the statistical equilibrium populations (several hundred levels per ion), and the non-thermal cascade of Compton electrons produced by radioactive decays. The most computationally expensive part if the radiative transfer which we perform line-by-line in about 300,000 lines in supernovae and even larger numbers for kilonovae. We have used the combination of our own Dardel partition with previous allocations to compute models that have led to over a dozen high-cited publications (see activity reports). Over the next 12 months, we aim to compute several sets of new models both in 1D and 3D. For supernovae in 3D, post-doc Bart van Baal is currently working on Type II (hydrogen-rich) explosions, following completion and publication of grids of Type I models. PhD student Stan Barmentloo is meanwhile exploring the recently opened infrared regime with new 1D models. For kilonovae, PhD student Blanka Vilagos is set to compute several 3D hydrodynamic models recently produced by our collaborators in Hamburg.