All seats in the opera house's 1,200-capacity auditorium will now be available for performances between 19 July and 29 August, with additional tickets to Mozart's Così fan tutte, Verdi"s Luisa Miller, Wagner's Tristan und Isolde and three concerts by the Orchestra of the Age of Enlightenment.
Ensuring the safety of its audiences remains Glyndebourne's top priority.
The Sussex-based opra house is strongly encouraging the continued use of face coverings in the auditorium, in line with the theatre industry's 'See it safely' guidance.
A number of other safety measures will remain in place for Festival 2021 performances from 19 July onwards, including temperature testing, enhanced cleaning and contactless ticketing.
Glyndebourne chose to invest in a loss-making Festival this year in order to protect jobs and provide work to freelance artists, technicians and craftspeople.
Every additional ticket that is sold this summer will support Glyndebourne's long-term survival.
Public booking for the additional tickets will open at 10.00am on Sunday 18 July from glyndebourne.com