We present a genome assembly from an individual male Hypsopygia costalis (the Gold Triangle; Arthropoda; Insecta; Lepidoptera; Pyralidae). The genome sequence is 818 megabases in span. Most of the assembly is scaffolded into 31 chromosomal pseudomolecules with the Z sex chromosome assembled. The mitochondrial genome has also been assembled and is 15.3 kilobases in length. Gene annotation of this assembly on Ensembl identified 19,248 protein coding genes.