Can you explain the recent US visa regulation changes related to one holders and four-year stay limits?

It depends - the proposed US visa regulation changes are not yet finalized.

The US Department of Homeland Security has suggested replacing the current "Duration of Status" (D/S) system with a fixed stay period for most F-1 and J-1 visa holders, typically up to four years. If your academic program extends beyond this, you would need to apply for an extension through USCIS.

Other proposed changes include:
- Reducing the F-1 post-completion grace period from 60 days to 30 days
- Capping English-language training at 24 months
- Restricting undergraduate transfers in the first year and limiting graduate student transfers or changes in study objectives

These rules are still under review and not yet in effect. The current D/S system remains until any new rules are officially published and a start date is announced.