Genome editing technology is evolving fast, and many labs worldwide are generating crop plants with improved traits. If transgenes were used to generate the edits, foreign DNA must be effectively removed by outcrossing. After an evaluation of various technologies, we show that long-read whole-genome sequencing (WGS) is at present the only reliable approach to confirm the absence of foreign DNA. We suggest using long-read WGS before requesting exemption from classification as genetically modified organisms and provide a guide for interpreting WGS data.