Optional Practical Training (OPT) allows F-1 students to gain employment experience in their field of study. Key changes to OPT rules include extending the duration of OPT from 12 months to 29 months for STEM students, allowing students to apply for OPT up to 90 days before and 60 days after completing their degree, and eliminating the H-1B "Cap Gap" issue for OPT students with an approved H-1B petition.