How does the STEM OPT extension work?

If your degree is on the government's STEM designated-degree list, you can generally extend your 12 months of post-completion OPT by a further 24 months — three years of work authorisation in total. Requirements include an employer enrolled in E-Verify, a formal training plan (Form I-983), and reporting obligations you must keep up with. It is also how many people get multiple attempts at the H-1B lottery. Full details and current rules are on USCIS.gov.