diff --git a/structuredefinitions/Extension-UKCore-EffectivePeriod.xml b/structuredefinitions/Extension-UKCore-EffectivePeriod.xml
index 65a65b32..2152ed62 100644
--- a/structuredefinitions/Extension-UKCore-EffectivePeriod.xml
+++ b/structuredefinitions/Extension-UKCore-EffectivePeriod.xml
@@ -6,7 +6,6 @@
   <name value="ExtensionUKCoreEffectivePeriod" />
   <title value="Extension UK Core Effective Period" />
   <status value="retired" />
-  <experimental value="false" />
   <date value="2021-09-10" />
   <publisher value="HL7 UK" />
   <contact>