H-1B selected in March. OPT expires in July. H-1B starts October 1. Cap-gap is what keeps you legal and employed for those 3 months. Here's the exact playbook.
Cap-gap is codified in 8 CFR 214.2(f)(5)(vii). When an F-1 student's employer timely files a nonfrivolous H-1B change of status petition (Form I-129) with a start date in the fiscal year (usually October 1), cap-gap provides two automatic extensions, both lasting until the H-1B starts and no later than April 1 of that fiscal year:
This is not an application, it's automatic. You do not file any additional form with USCIS. However, you must get your DSO to issue an updated I-20 with cap-gap notation. This I-20, combined with your original EAD and the H-1B receipt notice, is your proof of authorized work and status during cap-gap.
Your OPT EAD is still valid on April 1 (or whenever your employer files). Cap-gap automatically extends your work authorization until the H-1B starts, no later than April 1 of the fiscal year. Continue working normally. Update I-20 with DSO.
Your EAD expires in June but your H-1B petition was already filed before expiration. Cap-gap kicks in, your work authorization continues until the H-1B starts (no later than April 1 of the fiscal year) even though your EAD is 'expired.' The cap-gap period is what authorizes work, not the EAD card.
If your employer withdraws the petition or USCIS rejects, denies or revokes it during cap-gap, the cap-gap extension ends. Stop working and ask your DSO and an immigration attorney the same day what your status is and what options you have.
This is where students make costly mistakes. Cap-gap is a status protection, it keeps you in legal status inside the US. It does not give you a travel document or the ability to return to the US from abroad.
If you leave the US during cap-gap, you cannot re-enter on your OPT EAD or F-1 status, cap-gap status does not exist outside US borders. To re-enter, you need an H-1B visa stamp, which you'd have to get at a US consulate abroad. But you may not yet have an approval notice (just a receipt) if USCIS is still processing. And consular appointments can take weeks or months.
The practical risk: you travel for a wedding in India in August, you're abroad during cap-gap, your H-1B is still pending, and you can't get a consular appointment until November. You're stuck. Don't travel during cap-gap unless you have an H-1B visa stamp already in your passport.
For I-9 verification during cap-gap, present the following combination:
Sumit covers the critical F-1 to H-1B transition period including OPT, STEM OPT, cap-gap, and the H-1B lottery process for international students at US universities.