diff --git a/include/openthread/instance.h b/include/openthread/instance.h
index 4f69083f6..d32eb65d8 100644
--- a/include/openthread/instance.h
+++ b/include/openthread/instance.h
@@ -45,6 +45,16 @@
 extern "C" {
 #endif
 
+/**
+ * The OpenThread API monotonic version number.
+ *
+ * This number MUST increase by one each time the contents of public OpenThread API include headers change.
+ *
+ * @note This number versions both OpenThread platform and user APIs.
+ *
+ */
+#define OPENTHREAD_API_VERSION (1)
+
 /**
  * @addtogroup api-instance
  *