Due to the coronavirus pandemic, Costa Rica has on several occasions extended tourist visas beyond the typical 90-day limit. Barring further changes, that grace period is set to expire in June.
The current policy reads as follows:
[The Immigration Administration] has authorized for the last time until June 1, 2021, the extension of the legal permanence of foreigners who have entered the country as tourists as of December 17, 2019. This will be the last extension of legal permanence under the subcategory of Tourism.
In order to obtain the benefit of this exception, the foreign person must send proof of their travel insurance to the electronic address seguro@ict.go.cr.
In other words, anyone who entered Costa Rica as a tourist after December 17, 2019, can legally stay in Costa Rica until June 1, 2021, regardless of the length of the visa stamp indicated in their passport.
Unless there is a last-minute change to policy, as of June 1 all tourists must leave Costa Rica before the time indicated by their visa stamp (i.e. within 90 days at a maximum).
Having an irregular immigration status carries various legal penalties that can include being banned from re-entry to Costa Rica.