Proprietors of and applicants for European patents have the possibility to opt out their European patents or patent applications from the exclusive competence of the Unified Patent Court (UPC). An opt-out most notably prevents a competitor from challenging the validity of the European patent centrally before the UPC (by filing an action for revocation before the UPC), thus allowing the proprietor to avoid putting all his eggs (i.e., all national parts of the European patent) in one basket.
The possibility to opt out is open until one month before the end of a seven-year transitional period after the entry into force of the UPC Agreement (UPCA) on June 1, 2023 but is no longer available if an action has already been brought before the UPC. The possibility to opt out is not available for European patents with unitary effect, which are also called "unitary patents". An opt-out can be withdrawn at any time "unless an action has already been brought before a national court".