This study provides the first comprehensive genomic surveillance of critically important antimicrobial (CIA)-resistant Escherichia coli in companion animals, addressing gaps in the understanding of antimicrobial resistance (AMR) transmission dynamics and the environmental dissemination of hazardous resistance genes within urban ecosystems. A total of 244 CIA-resistant Escherichia coli (CIA-EC) isolates were obtained from 730 anal swabs collected across 11 pet hospitals in Shanghai. High-risk zoonotic clones, such as ST410 and ST405, were identified across multiple districts, with bla