diff --git a/modules/network-observability-flowmetric-api-specifications.adoc b/modules/network-observability-flowmetric-api-specifications.adoc
index 09e4b3b44654..c9adb00fb33c 100644
--- a/modules/network-observability-flowmetric-api-specifications.adoc
+++ b/modules/network-observability-flowmetric-api-specifications.adoc
@@ -107,6 +107,11 @@ When set to `Egress`, it is equivalent to adding the regular expression filter o
 be used to eliminate duplicates: `Duplicate != "true"` and `FlowDirection = "0"`.
 Refer to the documentation for the list of available fields: https://docs.openshift.com/container-platform/latest/observability/network_observability/json-flows-format-reference.html.
 
+| `flatten`
+| `array (string)`
+| `flatten` is a list of list-type fields that must be flattened, such as Interfaces and NetworkEvents. Flattened fields generate one metric per item in that field.
+For instance, when flattening `Interfaces` on a bytes counter, a flow having Interfaces [br-ex, ens5] increases one counter for `br-ex` and another for `ens5`.
+
 | `labels`
 | `array (string)`
 | `labels` is a list of fields that should be used as Prometheus labels, also known as dimensions.