Red-shifted bioluminescence reporters are desirable for biological imaging. We describe the development of red-shifted luciferins based on synthetic coelenterazine analogs and corresponding mutants of NanoLuc that enable bright bioluminescence. One pair in particular showed superior in vitro and in vivo sensitivity over commonly used bioluminescence reporters. We adapted this pair to develop a bioluminescence resonance-energy-based Antares reporter called Antares2, which offers improved signal from deep tissues.